Henry T. (Henry Thomas) De La Beche.

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the little attrition it could have suffered during its transport from the
higher Alps to its present position.

Fig. 104.



-:~




A large amount of information has been obtained respecting the dis-
tribution of erratic blocks in Northern Europe, and the sources in Scan-
dinavia whence they have been detached.* The area over which they
have been so distributed has been shown in a map by Sir Roderick
Murchison, M. de Verneuil, and Count Keyserling,f the boundary line
exhibiting the southern and eastern limits of the erratic blocks extend-
ing from Prussia to Voroneje, in Russia, and thence northwards to the
Gulf of Tcheskaia, on the North Sea. It is remarked that from the
German Ocean and Hamburg on the west, to the "White Sea on the
east, an area of 2000 miles long, varying in width from 400 to 800
miles (which may, perhaps, be roughly estimated at about 1,200,000
square miles), is more or less covered by loose detritus, amid which
there are blocks of great size, the whole derived from the Scandinavian
mountains.

"While regarding the kind and extent of country thus more or less

* The observer would do veil to consult the Rapport sur un Mdmoire de M. Durocher,
intituld " Observations sur le Phe*nomene Diluvien dans le Nord de 1'Europe," by M.
Elie de Beaumont (Comptes Rendus, torn. xiv. p. 78, 1842), wherein an excllent sum-
mary and general view of the subject, including the marking of subjacent rocks, up to
the date of the observations, will be found. He should likewise consult the " Geology
of Russia in Europe, and the Ural Mountains," 1845, by Sir Roderick Murchison, M.
de Verneuil, and Count Keyserling; chapter xx., Scandinavian Drift and Erratic Blocks
in Russia; and chapter xxi., Drift and Erratic Blocks of Scandinavia, and Abrasion
and Striation of Rocks; and also the " Ilistoire des Progres de la Gdologie de 1834 a
1845," torn. ii. premidre partie, Terrain Quaternaire ou Diluvien. Formation erratique
du Nord de 1'Europe. Paris, 1848. Notwithstanding the title, this valuable work
contains information up to the date of publication. A most excellent and impartial
summary of the labours relating to this subject, with original observations, will be found
in this "History."

f "Geology of Russia in Europe and the Ural Mountains," 1845.



DERIVED FROM SCANDINAVIA. 279

covered with erratic blocks and the position which the Scandinavian
mountains would occupy relatively to a large submerged area, the opi-
nion that glaciers, icebergs (detached from them), and coast ice, may
have been the chief means of dispersing the blocks and other detritus
from a large isolated region, as that of Scandinavia would then be, ap-
pears far from improbable. Careful examinations of the Scandinavian
region itself, shows that the whole land has been elevated above the
present level of the adjoining seas in comparatively recent geological
times, and there has been found a scoring of subjacent rocks and dis-
persion of blocks outwards from it, according with this view.*

In the region occupied by these erratic blocks, ridges of them and
other detrital matter have been observed to run in lines, often for con-
siderable distances. These are commonly known as skdrs, or osars.^
Count Rasoumouski would appear (in 1819) to have been among the first
to remark upon those in Russia and Germany, observing that they
usually occurred in lines having a direction from N.E. to S.W. M.
Brongniart pointed out (in 1828), that those of Sweden, though some-
times inosculating, took a general direction from north to south. J Much
discussion has arisen respecting the origin of these lines of accumula-
tion. Upon the supposition that lines of blocks may have been accu-
mulated by glaciers, and the drift of iceberg and coast ice in particular
directions, and that upon the uprise o,f such lines of deposits, breaker
action would be brought to bear upon them for a time, we should expect
very complicated evidence.

In Northern America erratic blocks are found to occupy a large area,
some being strewed as far south as 40 N. latitude. Here, as in northern

* M. Daubree states (Comptes Rendus, vol. xvi. 1843), that the traces of transport of
detritus and of friction, diverge from the high regions, precisely as in the Alps. This
was observed up to an elevation of 3800 feet (English). M. de Bohtlingk (Poggendorff's
Annalen, 1841), states that Scandinavian blocks have been transported from the coast
of Kemi into the Bay of Onega, and from Russian Lapland into the Icy Sea, that is, in
northerly, northwesterly, and northeasterly directions, as quoted also in the "Geology
of Russia," vol. i. p. 528.

f It is worthy of remark that similar accumulations of this date, in Ireland, are
known as Escars.

I " Annales des Sciences Naturelles," 1828. M. d'Archiac observes ("Histoire des
Progres de la Geologic," 1848, torn. ii. p. 36), that " the form of the osars, their dis-
position, and their parallelism with the furrows and scratches of erosion, naturally lead
to the idea of a current which has swept the southern part of Sweden from N.N.E. to
S.S.W. M. Durocher has found, with M. Sefstrom, that the osars were heaped up on
the southern side of the mountains, which, in that direction, opposed their course. The
osars in Finland, though less marked, have a direction from N. 25 W. to S. 25 E.,
one, which, with the preceding, represents the radii of the semicircle in which the great
erratic block deposit of Central Europe occurs."

In the "Geology of Russia in Europe and the Ural Mountains," will be found the
views of its authors respecting sk'ars or osars. A figure is given of an iceberg aground,
and the consequences of its melting stated, lines of angular and rounded blocks being
strewed, as the ice dissolved, by a current acting constantly in one direction.



280 ERRATIC BLOCKS OF NORTH AMERICA.

Europe, the general drift of detritus appears to be from the northward
to the southward, and blocks perched at various altitudes, scored and
scratched surfaces of subjacent rocks, and osars or lines of accumulation,*
occur in the same manner. Such similar effects point to similar causes,
and hence the explanations offered have been of a similar general cha-
racter.f A large amount of information has also been collected respect-
ing the occurrence of these blocks, and of the polishing and scoring of
subjacent rocks.J It is stated that the divergence of any blocks, such,
for example, as those of the Alps, is not observed in the United States.
Professor Henry Rogers points out that the scorings do not radiate
from the high grounds, but that amid the mountains of New England,
and in the great plains of the west, and in Pennsylvania, Vermont, and
Massachusetts, they preserve a southeast direction at all their elevations ;
the lower parts of the great valleys being alone excepted. In the moun-
tainous portions of the region, the heights and flanks exposed to the
north and northwest, are the most polished and scored. Blocks of large
size have been found in New England, New York, and Pennsylvania,
from 1000 to 1500 feet above the sea.

Erratic blocks are also found in South America. Mr. Darwin dis-
covered them up the Santa Cruz River, Patagonia, in about 50 10' S.
latitude, and about 67 miles from the nearest Cordillera. Nearer the

* An interesting account of two remarkable trains of angular erratic blocks in Berk-
shire, Massachusetts, is given by Professors Henry and William Rogers, in the " Boston
Journal of Natural History," June, 1846. These two trains, one extending for 20 miles,
both previously noticed by Dr. Reid and Professor Hitchcock, were traced to their
{sources. The blocks are generally large, the smaller being several feet in diameter.
One weighs about 2000 tons. The blocks gradually decrease in size to the S.E., those
which have travelled farthest being the most worn. They are stated not to mingle with
the general drift beneath them, the boulders and pebbles in which bear " the traces of
a long-continued and violent rubbing." " Other long and narrow lines of huge erratic
fragments are seen elsewhere in Berkshire, and abound, we think, in nearly all the
mountainous districts of New England. One such train, originating apparently in the
Lennox ridge, about two miles on the south of Pittsfield, crosses the Housatonic Valley,
southeasterly, as far at least as the foot of the broad chain of hills in Washington. Some
very extensive ones are to be seen on the western side of the White Mountains."

f These will be found in the works and memoirs of Hitchcock, Mather, Emmons, Hall,
Rogers, Hubbart, Redfield, Jackson, Christy, Ch. Martins, and other geologists.

J We are indebted to Dr. Bigsby for an early notice of the erratic blocks of North
America. (Trans. Geol. Soc., London, vol. i., second series.)

In 1833, Professor Hitchcock (Report on the Geology of Massachusetts, Art. Dilu-
vium) adduced abundant evidence of the northern origin of these blocks in the districts
described by him. The like was also done at an early date for other portions of North
America, by Messrs. Lapham, Jackson, Alger, and others. The observer will find an
able summary of the facts known in 1846, on this subject, in Professor Hitchcock's
Address to a meeting of the Association of American Geologists in that year. Professor
Henry Rogers also treated in a general manner of the American erratic blocks in his
Address to the same scientific body in 1844, (American Journal of Science, vol. xlvii.)
Another general summary, up to 1848, is given by the Vicomte d'Archiac (Histoire des
Prog res de la G6ologie, torn, ii., chap. 9, Terrain Quaternaire de TAmdrique du Nord).



ERRATIC BLOCKS OF SOUTH AMERICA. 281

mountains (at 55 miles) they became "extraordinarily numerous." One
square block of chloritic schist measured 5 yards on each side, and
projected 5 feet above the ground ; another, more rounded, measured
60 feet in circumference. " There were innumerable other fragments
from 2 to 4 feet square."* The great plain on which they stood was
1400 feet above the sea, sloping gradually to sea clifis, of about 800
feet in height. Other boulders were found upon a plain, above another,
elevated 440 feet, through which the same river flows, and at 800 feet
above the sea. In the valley of the Santa Cruz, and at 30 or 40 miles
from the Cordillera (the highest parts in this latitude rise to about 6400
feet), blocks of granite, sienite, and conglomerate, not found in the
more elevated plains, were detected. Mr. Darwin infers that these
are not the wreck of those observed on the higher plain, but that they
have been subsequently transported from the Cordillera. He had not
opportunities of observing other erratic blocks in Patagonia, but refers
to the great fragments of rocks noticed by Captain King on the surface
of Cape Gregory, a headland, about 800 feet high, on the northern
shore of the Strait of Magellan. Mr. Darwin also describes rock
fragments of various dimensions and kinds in Tierra del Fuego and the
Strait of Magellan, amid stratified and unstratified accumulations of a
similar general character to those of this geological date in Europe. f
Many of the erratic blocks are large, one at St. Sebastian's Bay, east
coast of Tierra del Fuego, was 47 feet in circumference, and projected
5 feet from the sand beach. The general drift of these deposits is
considered to be from the westward, the manner in which the trans-
ported fragments of rock would be carried by a current similar to that
which sweeps against the present land. On the north of Cape Virgins,
.close outside the Strait of Magellan, the imbedded fragments are con-
sidered to have been transported 120 geographical miles or more from the
west and southwest. On the northern and eastern coasts of the Island
of Chiloe, extending from 43 26' to 41 46' S. latitude, Mr. Darwin
detected an abundance of granite and sienite boulders, from the beach

* Darwin, " On the Distribution of Erratic Boulders, and on the Contemporaneous
Unstratified Deposits of South America." Geol. Trans., second series, vol. vi. p. 415.

f At Elizabeth Island, Straits of Magellan, there occurs "fine-grained, earthy or
argillaceous sandstone, in very thin, horizontal, and sometimes inclined laminae, and
often associated with curved layers of gravel. On the borders, however, of the eastern
parts of the Strait of Magellan, this fine-grained formation often passes into, and
alternates with great unstratified beds, either of an earthy consistence and whitish
colour, or of a dark colour and of a consistence like hardened coarse-grained mud, with
the particles not separated according to their size. These beds contain angular
and rounded fragments of various kinds of rock, together with great boulders." Geol.
Trans., second series, vol. vi. p. 418. Variations of these accumulations are noticed
as occurring in other places, and two sections of contorted and confused beds at Gre-
gory Bay are given, and Mr. Darwin infers that this disturbance may have been pro-
duced by grounded icebergs.



282 MOLLUSC REMAINS IN SUPERFICIAL DETRITUS.

to a height of 200 feet on the land. He infers that these boulders have
travelled more than 40 miles from the Cordillera on the east.*

Upon the supposition of the submergence of a large portion of the
present dry land of Northern Europe, Asia, and America, beneath seas
upon which ice was formed, and into which glaciers protruded in lower
latitudes than at present, we should expect to discover in the marine
deposits of these regions and of the period, now upraised into the atmo-
sphere, evidences of the marine animal life of the time having corre-
sponded with the low temperature to which it was then exposed. This
evidence is considered to have been found.

As regards the British Islands, Mr. Trimmer pointed out in 1831,
that amid the detrital accumulations referred to this date, and at a
considerable height above the sea (since ascertained to be 1392 feet),
upon Moel Trefan (one of the hills on the outskirts of the chief Caernar-
vonshire mountains), fragments of Buccinum, Venus, Natica, and Turbo
of existing species were found. He also stated that on the flanks of
the Snowdonian mountains, and between them and the adjoining sea, in
the Menai Straits, there were large accumulations of boulders and
fragments derived from a distance (among them chalk flints), mingled
with others of a local kind. Mr. Trimmer subsequently (1838), pub-
lished a more general statement on the same subject, noticing various
localities where he and others had found shells of a similar character
in deposits referring to this date.f

Commenting on the facts observed by Mr. Trimmer on Moel Trefan,
Sir Roderick Murchison (in 1832) inferred from the previous discovery
of shells of existing species in the Lancashire gravels and sands by Mr.
Gilbertson, one which he was enabled to confirm from actual observa-
tion, and from finding similar accumulations over a large tract of
country, that the materials of the ancient shore 'of Lancashire and of
the estuary of the Kibble, were deposited during a long-protracted
period, and " were elevated and laid dry after the creation of many of

* " The larger boulders were quite angular." ..." One mass of granite at Chacao
was a rectangular oblong, measuring 15 feet by 11 feet, and 9 feet high. Another, on
the north shore of Lemuy islet, was pentagonal, quite angular, and 11 feet on each
side; it projected about 12 feet above the sand, with one point 16 feet high: this
fragment of rock almost equals the larger blocks on the Jura." Geol. Trans., second
series, vol. vi. p. 425.

f The first communication was made to the Geological Society of London (Proceed-
ings of that Society, vol. i.) ; the second to the Geological Society of Dublin, in a me-
moir, in two parts, entitled, "On the Diluvial or Northern Drift on the Eastern and
Western side of the Cambrian Chain, and its connexion with a similar Deposit on the
Eastern side of Ireland, at Bray, Howth, and Glenismaule." (Journal of the Geolo-
gical Society of Dublin.) Mr. Trimmer mentions that, prior to his discovery of the
shells on Moel Trefan, Mr. Gilbertson had found shells of existing species in gravel
and sand near Preston, Lancashire, and that Mr. Underwood had observed furrows and
scratches on the surface of rocks laid bare among the Snowdonian mountains, whca
the great road from Bangor to Shrewsbury was in progress.



MOLLUSC REMAINS IN SUPERFICIAL DETRITUS. 283

the existing species of molluscs."* Numerous facts of the like kind
were noticed by different observers,! hut the inference as to a tempera-
ture less at that geological time than at present, as shown by the
remains of molluscs, does not appear to have taken a distinct form
until Mr. Smith, of Jordan Hill, published his views on the subject in
1839. J He discovered shells in places where their animals had lived
and died, in the counties of Lanark, Renfrew, and Dumbarton, and
hence inferred their entombment by depression, a half-tide deposit
being converted into one in a deeper sea. From these and other
researches, Mr. Smith obtained a mass of evidence which led him to
conclude from the remains of the molluscs discovered in deposits of this
date in different localities, that the climate of the British Islands had
then been colder than it now is, more especially as Arctic molluscs,
not now found round the British coasts, were obtained from these accu-
mulations^

* Address, as President, to the Geological Society of London, February, 1832. Pro-
ceedings of that Society, vol. i. p. 366.

f Among the observations of the time, and as important for the locality noticed,
should be mentioned those of Sir Philip Egerton, "On a bed of gravel containing
Marine Shells of recent Species, at Wellington, Cheshire" (Proceedings of the Geolo-
gical Society, vol. ii. p. 189, April, 1835). Sir Philip notices the remains of Turritella
terebra, Cardium edule, and Murex arcnaceus, and infers that there had been an altera-
tion of 70 feet in the level of land and sea, as regards the locality, since the deposit
was formed. In 1837, Mr. Strickland ("On the Nature and Origin of the various
kinds of transported Gravel occurring in England," read at the British Association in
that year) took a general view of the stratified and unstratified character of these
deposits, and divided them into 1. Marine drift, formed when the central portions of
England were under the sea ; and, 2. Fluviatile drift, when they were above its level,
forming dry land, the first composed of (a) erratic gravel, without chalk flints ; (bj
erratic gravel, with chalk flints ; and (c) local, or non-erratic gravel.

J "On the late changes of the Relative Levels of the Land and Sea in the British
Islands," (Memoirs of the Wernerian Natural History Society, Edinburgh, vol. viii. p.
49, &c.) In this memoir Mr. Smith most carefully cites all those who had previously
discovered facts relating to the subject, giving an account of these facts.

g Alluding to the researches of M. Deshayes, to whom the unknown shells discovered
were transmitted, and who stated that those still found recent, but not in the British
seas, occur in northern latitudes, Mr. Smith remarks that this view confirmed that
which he had previously entertained from finding many of the shells common with
those obtained by Sir Charles Lyell, at Uddevalla, in Sweden, and figured by him
(Phil. Trans. 1835) ; from having been informed by the same geologist that the
Fusus Peruvianus still inhabited the Arctic seas ; and from Mr. Gray (of the British
Museum) having, from a cursory examination of the shells discovered, remarked that
they had all the appearance of Arctic shells. Mr. Smith adds, " In the Clyde-raised
deposits, shells common to Britain and the northern parts of Europe occur in much
greater abundance than they do at present. The Pecten islandicus, which has probably
entirely disappeared, and the Cyprina islandica, which, if found recent in the Clyde,
is extremely rare, are amongst the most common of the fossil species." Most valuable
catalogues are appended to the memoir of Mr. Smith, consisting of lists of recent shells
in the basin of the Clyde and north coast of Ireland (including land and fresh-water
shells) ; of shells from the newer Pliocene deposits of the British Islands (also including
land and fresh-water shells) ; and of recent species (then new) from the Frith of Clyde.



284 EVIDENCE OF A COLDER CLIMATE IN BRITAIN,

Professor Edward Forbes, in 1846, availing himself of the informa-
tion then existing, and of his own researches on the same subject,
pointed out that the total number of species of molluscs discovered in
the deposits of the British area and referred to this geological time,
was about 124, all, with a few exceptions now existing in the seas
around the British Islands, and yet indicating by their mode of assem-
blage a colder state of the area than at present.* While carefully
noticing the error which might arise from neglecting the occurrence of
species at different depths in the sea, he observes, that among those
found in these deposits, and in situations where they must have lived
and died, there are shells, such as the Littorince, the Purpura, the
Patella, and the Lacunce, "genera and species definitely indicating,
not merely shallow water, but in the first three instances, a coast
line."t

* Professor E. Forbes, " On the Connexion between the Distribution of the existing
Fauna and Flora of the British Isles, and the Geological Changes which have affected
their Area during the Period of the Northern Drift," (Memoirs of the Geological Survey
of Great Britain, vol. i. p. 367, &c.) The Professor observes, that, "as a whole, this
fauna is very unprolific, both as to species and individuals, when compared with the
preceding molluscan fauna of the red and coralline crags, or that now inhabiting our
seas and shores. This comparative deficiency depends not on an imperfect state of our
knowledge of the fossils in the glacial formations : on that point we now have ample
evidence ; but on some difference in the climatal conditions prevailing when those beds
were deposited. Such a deficiency in species and individuals of the testaceous forms
of mollusca, indicates to the marine zoologist, the probability of a state of climate
colder than that prevailing in the same area at present. Thus the existing fauna of
the Arctic seas include a much smaller number of testaceous molluscs than those of
Mid-European seas, and the number of testacea in the latter is much less than in South-
European and Mediterranean regions. It is not the latitude, but the temperature which
determines these differences." " That the climate," he subsequently observes, " under
which the glacial animals lived, was colder, is borne out by an examination of the spe-
cies themselves. We find the entire assemblage made up, 1st, of species (25) now living
throughout the Celtic region in common with the northern seas, and scarcely ranging
south of the British Isles ; 2d, of species (24) which range far south into the Lusitanis
and Mediterranean regions, but which are most prolific in the Celtic and northern seas ;
3d, of species (13) still existing in the British seas, but confined to the northern poi
tion of them, and most increasing in abundance of individuals as they approach towards
the Arctic circle ; 4th, of species (16) now known living only in European seas, north
Britain, or in the seas of Greenland and Boreal America ; 5th, of species (6) not noi
known existing, and unknown fossil in previous deposits. Two other species, froi
southern deposits in Ireland, were, one the same as one (Turritella incrassata) still exh
ing in the South-European, though not in the British seas, and the other (Tornate
pyramidata) extinct, but found fossil in the crag." Professor E. Forbes remarks, that
it is " of consequence to note the fact that the species most abundant and generally
diffused in the drift are essentially northern forms, such as Astarte elliptica, compress
and borealiSj Cyprina communis, Leda rostrata, and minuta, Tellina calcarea, Modiola
garis, Fusus bamfius, and scalar if or mis, Littorince and Lacunce, Natica clausa and Bnccini
undatum ; and even Saxicava rugosa and Turritella terebra, though widely distributed,
much more characteristic of north European than of southern seas."

f " Memoirs of the Geological Survey of Great Britain," vol. i. p. 370. The
fessor adds, "a most important fact, too, is that among the species of Litlorina,



FROM MOLLUSC REMAINS AND EXISTING FLORA. 285

Taking a general view of the flora of the British Islands, and of the



Online LibraryHenry T. (Henry Thomas) De La BecheThe geological observer → online text (page 32 of 85)