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IC-NRLF




BRARY

OF



ALIFORNIA



ICQ
RY



-

REESE LIBRARY

OF THE

UNIVERSITY OF CALIFORNIA.

Received.

Accessions No,



80






ENGINEEBING GEOLOGY,



FIELD GEOLOGY



LIBRARY

UNIVERSITY OF

CALIFORNIA.



>



ENGINEERING GEOLOGY,



BY



W. HENRY PENNING, F.G.S.,

GEOLOGIST, H. M. GEOLOGICAL SURVEY OF ENGLAND AND WALES.
AUTHOR OF ' FIELD GEOLOGY,' ETC.



WITH 1LLUSTRA TIONS AND COLOURED PLA TES.




LONDON :

BAILLIERE, TINDALL, AND COX,
20, KING WILLIAM STREET, STRAND.

1880.
[All Riyhl* Reserved.}



Q E 33



EAWTH

SCIENCES

LIBRARY



AS A SLIGHT TRIBUTE OF ESTEEM

THIS WORK

IS INSCRIBED WITH THE NAME OF

CHAELBS HUTTON GEEGOEY, C.M.G.,

(PoM President of the Institution of Civil Engineers),

UNDER WHOM THE AUTHOR WAS PRIVILEGED TO

OBTAIN HIS EARLIER EXPERIENCES

IN ENGINEERING.



P KEF ACE.



THIS work first appeared, during 1879, in the pages of
Tlie Engineer as a series of articles upon Engineer-
ing Geology, which are now reproduced slightly
altered in form, considerably enlarged, and more fully
illustrated.

Engineering and Geology are so evidently and so
intimately related that a knowledge of the former
must include, and is incomplete without, an acquaint-
ance with the latter; in turn, Geology derives much
aid from engineering works, records and researches.

It is as an art that Geology must be treated for its
results to be of immediate practical value to engineers ;
but as all art is based upon definite laws or principles,
he will derive most benefit from Geology, and be the
most proficient in its practical application, who founds
his work upon it, also, as a science.

W. HENRY PENNING.



GRANVILLE HOUSE,

FINSBURY PARK, LONDON.

January, 1880.



CONTENTS.



PART I.

GEOLOGICAL STEATA, THEIE NATURE AND RELATIONS, AND
THEIR BEARING UPON PRACTICAL WORKS.

CHAPTER I.

PAGE

INTRODUCTION - 1

CHAPTER II.

GEOLOGICAL STRATA.

Geological Strata. Nature of the Rocks. Relations of
the Rocks. Bearing of the nature of the Rocks upon
practical works Railways Tunnels Embankments
Bridges - 8

CHAPTER III.
GEOLOGICAL STEATA (continued).

Bearing of the nature of the Rocks upon practical works,
continued Materials Minerals Metals Agriculture
Land-drainage Sewerage works - 28

CHAPTER IV.
GEOLOGICAL STRATA (continued].

Bearing of the relations of the Rocks upon practical works
Mining operations Railway cuttings Tunnels Em-
bankments Reservoirs Canals Main- drainage
Foundations Water-supply Dampness Disease - 41



CONTENTS.



PART II.

PROCEDURE IN THE FIELD.

CHAPTER I.

METHODS EMPLOYED IN GEOLOGICAL SURVEYING, MAPS
AND SECTIONS.

PAGE

Methods employed in geological surveying Determination
of rocks Tables - - 54

CHAPTER II.

METHODS EMPLOYED IN GEOLOGICAL SURVEY [NG

(continued).

Construction of geological maps Geological surveying
Example Dip - - 03

CHAPTER III.

METHODS EMPLOYED IN GEOLOGICAL SURVEYING

(continued).
Dip and strike Rules for finding dip Example - -72

CHAPTER IV.

METHODS EMPLOYED IN GEOLOGICAL SURVEYING

(continued}.
Example of surveying faulted area Drift deposits - 78

CHAPTER V.

METHODS EMPLOYED IN GEOLOGICAL SURVEYING

(continued).
Geological sections Practical value Levels -Filling in - 92



CONTENTS. XI



PART III.

ECONOMICS MATERIALS, MINERALS AND METALS;
SPRINGS AND WATER-SUPPLY.

CHAPTER I.

MATERIALS, MINERALS AND METALS.

PAGE

Economic products of the Recent and Tertiary Rocks - 99
CHAPTER II.

MATERIALS, MINERALS AND METALS (continued).

Economic products of the Secondary Rocks - 110

CHAPTER III.

MATERIALS, MINERALS AND METALS (continued}.

Economic products of the Palaeozoic Rocks - 125

CHAPTER IV.

SPRINGS AND WATER-SUPPLY.

Nature of Springs Surface Springs Deep- seated springs
Water-level - 131

CHAPTER V.

SPRINGS AND WATER-SUPPLY (continued).
Artesian Wells Absorption Wells - - 145

CHAPTER VI.
Building Sites ... - - 154



LIST OF ILLUSTRATIONS.



PLATE I. GEOLOGICAL MAP coloured - Frontispiece,

Figure J. Railway cutting in pervious and impervious

strata - - 45

2. Railway tunnel through a ridge - -47

3. Diagram to illustrate Rule for finding true dip - 75
4. Map of area geologically surveyed - 80

5. Section of strata - - 87

6. across area geologically surveyed - 97

J} 7. to illustrate the nature of springs and

their water-level -132

PLATE II. GEOLOGICAL SECTION coloured- - to face 140



ENGINEERING GEOLOGY,



PART I.

GEOLOGICAL STRATA, THEIR NATURE AND RELATIONS,
AND THEIR BEARING UPON PRACTICAL WORKS.



CHAPTER I.

INTEODUCTION.

IN the execution of engineering works, however scien-
tific in design and clever in workmanship, failure has
frequently usurped the place of success, because due
attention has not been paid to geological phenomena.
Numberless instances might be quoted in proof of this
proposition, whilst it is notorious that vast sums of
money have been thrown away in mining speculations
which would at once have been characterised as hope-
less by anyone possessing the slightest acquaintance
with the science of Geology. A late eminent authority
(Professor Jukes) has stated his belief that the amount
of money fruitlessly expended in a ridiculous search
after coal, even within his own experience, would have
paid the entire cost of the Government Geological
Survey of the United Kingdom.

Although a knowledge of this science is undoubtedly
a great acquisition, which affords both pleasure and

1



ENGINEERING GEOLOGY.



profit to its possessor, it is not possible, nor even de-
sirable, for all professional engineers to become pro-
ficient geologists. Those for whom this work is more
especially intended have too many claims upon their
time and attention to bestow either upon a study of
abstract principles, laws, and theories, which do not
relate to their own particular science, art, or occupa-
tion ; but they may nevertheless, and with advantage,
avail themselves of the labours of others, when the
results of those labours bear directly, and in a very
important degree, upon the stability or success of the
works designed or executed by them, or under their
superintendence.

The engineer should certainly make himself ac-
quainted with the geology of a district through which
a railway is to be constructed from his designs and
along the line of his selection. He should ascertain
the nature of the various rocks that will be met with,
not only at and near the surface of the ground, but for
a considerable distance below; their relation to each
other, and the important influence they will exert upon
the works in contemplation. * Trial-holes ' are generally
dug for this purpose, but these are simply pits exca-
vated to a depth of a few feet, and afford information
which, although valuable in itself, unless amplified in
a particular manner, extends only to the superficial
deposits. Deep borings are sometimes made, but are,
in most cases, too costly ; and however numerous these,
or trial-holes, may be, both fall far short of what can
be achieved in the same direction through the methods
employed by the field-geologist. By these are deter-
mined, not only the kind of rocks occurring at or near



INTRODUCTION.



the surface, but also their position in regard to each
other; and the geological surveyor is enabled co indi-
cate with reasonable accuracy what strata will be met
with to a depth, it may be, of several hundred feet,
and, what is of equal importance, the order of their
succession. These results of his labours include not
merely a knowledge of what beds would be pierced in
sinking a well, or in excavating trenches for founda-
tions, such as would be afforded equally by trial-holes
or borings of sufficient depth ; but they embrace also
the important points of the ' lie ' of the beds, the order
of their superposition, their outcrop, dip, and conse-
quent water-bearing properties ; by all of which the
stability and durability of engineering works are greatly
affected.

We cannot fail to perceive how differently placed or
constructed would have been many of the most im-
portant works, such as fortifications, railway-cuttings,
embankments, tunnels, and even sewers, had those who
designed them been acquainted with the principles,
methods, and results of field-geology; or how much
capital might have been usefully instead of fruitlessly
expended, or how many catastrophes would have been
averted. Mention has already been made of costly
sinkings for minerals, where they could not possibly
have been found; large sums of money have also been
wasted in equally fruitless searches for water. Yet
water-supply is as amenable to known laws as any*
other phenomenon of nature, and within certain limits
it may be determined without experiment. Although
the divining-rod has not even yet quite ceased to be a
power amongst us, its days are surely numbered; men

12



ENGINEERING GEOLOGY.



must, sooner or later, come to see that springs are
merely the result of water finding its own level, and
that for water to issue forth at one part of the earth's
surface, it must have been absorbed at another. When
the conditions affecting its absorption by and passage
through the strata of a district are known or can be
discovered, the existence of springs, their depth from
the surface, and the height to which they will ascend,
can be approximately, if not with extreme accuracy,
determined.

In his ' Rudimentary Geology/ Major- General
Portlock has truly and eloquently said : ' Geology
is now a true science, being founded on facts and
reduced to the dominion of definite laws, and in
consequence has become a sure guide to the practical
man. The miner finds in it a torch to guide him in
his subterranean passage, to the stratum where he
may expect to find coal or iron, or to the recovery of
the mineral vein which he has suddenly lost ; the
engineer is guided by it in tracing out his roads or
canals, as it tells him at once the firmest stratum for
supporting the one,, and the easiest to cut through for
the other, and makes him acquainted with the qualities
of the materials he should use in his constructions,
and the localities where he should seek them ; the
geographer finds his inquiries facilitated by learning
from geology the influence of the mineral masses on
the form and magnitude of the mountains and valleys,
and on the course of rivers ; the agriculturist is taught
the influence of the mineral strata on vegetable and
animal life, and the statesman discovers in the effects
of that influence a force which stimulates or retards



INTRODUCTION.



population; the soldier also may find in geology a
most valuable guide in tracing his lines both of attack
and defence ; and it is thus that a science rich in the
highest objects of philosophical research is at the same
time capable of the widest and most practical applica-
tion/

In the following pages, rules and methods relating
to stratigraphical geology only are given, as the
geological conditions which affect engineering and
similar works are, mainly, the extent of the various
strata, their lithological character, and their order of
succession. It matters not what may have been the
forms of Life during the ages when the strata were
deposited, what their relations to those older or more
recent, or what the order of their appearance in time ;
although the evidence regarding these points is as
strong and as interesting as any upon which is based
the science of Geology. The rocks are treated merely
as stones, clays, and sands of varying kinds ; some
possessing commercial value and great utility ; others
having qualities to be guarded against in all mechani-
cal operations ; some only exhibiting water-bearing
properties ; but all worthy of study, independently of
the old-world histories which they contain.

The names of places are given only in particular
instances, such as those of mines, important quarries,
notable sections, and so on, it having been considered
advisable not otherwise to refer to localities in the
description of the rocks. These are mentioned
generally, and under specific denominations, geological
maps indicating much more readily the formation at
any particular spot than a lengthy reference to the



6 ENGINEERING GEOLOGY.

many places which must otherwise have been men-
tioned as situated on an extended outcrop. Such
maps are generally too small for the boundaries of
formations to be defined upon them with extreme
accuracy ; indeed, they are not intended for that
purpose, but rather to indicate what set, or sets, of
beds an observer may expect to find in any particular
neighbourhood. When an accurate delineation is
required for any special purpose it may be found
upon the sheets (corresponding in size and index
numbers with the Ordnance maps) published by the
Government Geological Survey. These are laid down
upon a scale of one inch to a mile for the country
generally, and for some districts upon the large scale
of six inches to a mile ; their prices vary, of the former
(some of which may be obtained in quarter-sheets)
from 4s. to 8s. 6d. ; of the latter from 4s. to 6s. (p. 17),
The main object of this work is, however, to enable
the engineer to discover and, for all practical purposes,
to trace out for himself the nature and extent of the
rocks with which he is concerned.

An acquaintance with the methods of geological
surveying is the more valuable, because ' drifts' are
usually omitted from the maps ; these are a series of
superficial deposits which, although important in some
localities, are not shown on any of the older geological
charts, and are noticed on only a few of the more
recent official publications. They consist chiefly of
clays and gravels of peculiar character, which are
found here and there upon the older rocks, on hills
and in valleys, with no very definite mode of occur-
rence ; and although, as a rule, of no great thickness,



INTRODUCTION.



they of necessity exert a considerable influence over
all works constructed upon them. A section is
devoted to a brief description of these deposits, with
the methods of tracing and mapping them, as they
must also be treated from a practical point of view, in
the same way as the older and more generally impor-
tant formations.



LIBKAK v *

UNIVERSITY OF

CALIFORNIA.



CHAPTER II.

GEOLOGICAL STEATA.

Geological Strata. Nature of the Rocks. Kelations of the
Rocks. Bearing of the nature of the Rocks upon practical
works Railways Tunnels Embankments Bridges.

Geological Strata. The crust of the earth, consists of
a great number of alternating rocky layers, various in
kind, thickness, and extent, but always in regular, if
not in constant, sequence. The uppermost have been
formed in a great measure from the waste of those
beneath, in the same way as the material now being
deposited on the bottom of the sea has been derived
from the denudation of the present dry land. These
layers are but rarely horizontal, and they bear evidence
of having been subjected to some upheaving force
which has acted at various times, unequally and with
different degrees of intensity, beneath every portion of
the earth's surface. There have been corresponding,
and on the whole nearly equal, movements of depres-
sion, and all areas have frequently been dry land,
again to be covered by the waters of the ocean. It
is owing to this inequality in the upheaval of the
beds, and to their consequent partial destruction by



GEOLOGICAL STRATA.



the sea, that the lower and older strata are now
exposed at the surface of the ground, and that we
are enabled to classify the rocks and to decipher their
ancient history.

The formations, of which the denuded edges are thus
bared and thrown open to our inspection, are indicated
by different tints upon geological maps. If it be borne
in mind that each of the areas thus distinguished re-
presents, as a general rule, the edge and not the surface
of a formation, the proper apprehension of such maps
is much facilitated. It is evident that were the
variously-coloured portions each indicative of an origi-
nal surface-plane, the rocks so depicted would generally
be the newest, as overlying those which are hidden
beneath. But their edges only being exposed and
portrayed on the map, the main planes of bedding must
now be either in a vertical position, or inclined from
the surface in some direction, and the rocks, as a
matter of course, must pass in under some of those
that are contiguous. Geological maps show that, in
this country, by far the larger proportion of the edges,
or lines of outcrop, of the rocks, follow a nearly north
and south direction, therefore the beds must dip, if at
all, either to the east or to the west. The general dip
of the rocks in these islands is, on the whole, towards
the south-east ; consequently those on the north-west
are the oldest, and the lowest in the geological scale ;
those on the south-east are the highest in the scaie,
therefore the most modern.

All the beds of which ths various geological forma-
tions are composed are termed ' rocks/ whether they
are hard or soft, of aqueous or of igneous origin. The



10 ENGINEERING GEOLOGY.

following remarks have been as far as practicable
classified under three headings (a) The nature of the
rocks ; (b) The relation of the rocks to each other ;
(c) The bearing of the nature and relation of the rocks
upon practical operations.

(a) The Nature of the Rocks. The aqueous and
igneous deposits by which the known crust of the
earth has been built up, occur in successive layers, and
are of infinite variety as regards texture, colour, hard-
ness, and other peculiarities. All the rocks are made
up, wholly or in part, of minerals either in a crystalline
or fragmentary form, or of mineral matter in a state of
comminution. Some rocks contain metals, either in a
free or native state, or, as ores, in combination with
oxygen or sulphuric acid, whilst comparatively few are
without metallic colouration.

All rocks may be divided into two great classes :

1 . The igneous, or unstratified, which (formed below
the surface) were by volcanic or some similar force
erupted through or intruded into the pre-existing
formations. These are granites, traps and similar
rocks.

2. The aqueous, or stratified, which were deposited
from water as sediment, or (in some cases) as a
chemical precipitate. They are chiefly clays, sand-
stones, limestones, and gravels.

There are rocks which have been otherwise formed,
and some which have been altered from their original
condition by heat or pressure, or by both agencies
combined. Such metamorphic rocks may have been
either igneous or aqueous, but are principally of aque-



GEOLOGICAL STRATA. 11

ous origin, and are now found as gneiss, quartzites,
marbles, slates, schists, and altered ashes.

The class to which a rock belongs is practically im-
portant, on account of the difference in the normal
modes of its occurrence. The stratified rocks lie evenly,
the one upon the other, whether horizontally or not,
and preserve a regular but sometimes interrupted
sequence ; the unstratified follow no such definite lines,
but are found suddenly breaking through older rocks
and disappearing in an equally abrupt manner. In
both classes the rocks of every kind present many
varieties and gradations towards each other, but on the
whole they possess broad characteristics by which they
may be fairly determined. (See Some chapters on
Lithology, and Tables for the determination of rocks,
in 'Field Geology' (Bailliere), from which those in
Part ii. have been abridged.)

It may be noted that generally, but not without
exceptions, the older stratified and the altered rocks
are more crystalline and compact than are those of
more recent date. Those that were by an old classifi-
cation designated Primary, consist of slaty and crys-
talline strata, such as gneiss, and mica-schist, marble,
and clay-slate; Transition, of slaty and siliceous sand-
stones and calcareous shales ; Secondary, of chalk,
limestones, red sandstones, marls, and clays ; Tertiary,
of sands and clays; Recent, of sands, gravels, silt,
peat, and alluvium. The loose and friable beds are
the most recent, overlying others more consolidated of
secondary age, which in turn rest upon the more
crystalline primary strata. All were once in the same
unsolidified condition, but some have become hardened



12 ENGINEERING GEOLOGY.



> Trappean.



by chemical change and by the mechanical results of
pressure and infiltration, during the ages which have
elapsed since the time of their accumulation.
1. The more common igneous rocks are :

GEANITE. ~| ~

~ f Granitic.

SYENITE. 3

GABBEO. ' Greenstone.

FELSITE.

DOLEEITE. Basalt.

POEPHYEITE.

T- > V olcanic.

PHONOLITE.

TEACHYTE.



2. The aqueous rocks are :

Argillaceous.
CLAY.

SHALE. Hardened clay.

LOAM. Clay and sand, a mechanical admixture.
LIMESTONE when containing silicate of alumina : if

this be in sufficient proportion it constitutes an

hydraulic limestone.



Arenaceous.
SAND.

SANDSTONE. Consolidated sand, with siliceous, ferru-
ginous, or calcareous cementing material.
GEIT. Coarse sandstone.
GEAVEL.
CONGLOMEEATE. Consolidated gravel.



GEOLOGICAL STRATA. 13

Calcareous.

LIMESTONE. Sometimes earthy as Chalk, oolitic as
Bath freestone, crystalline as Marble.

MAGNESIAN LIMESTONE. Limestone composed of car-
bonate of lime and magnesia.

SILICEOUS LIMESTONE. Limestone containing much
silica, as in Kentish Rag.

The altered or metamorphic rocks are :

GNEISS. A foliated rock, otherwise similar to granite
in composition.

SCHIST. Sedimentary rock, altered and foliated.

QUAETZITE. Altered quartz sandstone.

SLATE. Clay altered and cleaved in a direction gene-
rally transverse to its original bedding.

There are many other rocks in each class, also
many which partake more or less of the character of
each, presenting infinite gradations ; but they occupy
comparatively small areas, and in other respects exert
the same influence as the rocks to which they are
most nearly allied, they may therefore, from an
engineering point of view, be considered as of slight
importance.

(&). The relation of the Rocks to each other. The
relation of the rocks of a district that is, their posi-
tion in regard to each other, their relative thickness,
dip, permeability, and so on is quite as important for
mechanical purposes as their individual nature. But
this relation, especially in a complicated area, is not
by any means readily ascertained, unless the proper



14 ENGINEERING GEOLOGY.

methods of procedure be understood. The thickness
of each necessarily rules the extent of ground it
occupies, but must be studied in connection with the
dip, which exercises also an influence on the shape of
the country quite as powerful as that of the nature of
the rocks of which it is composed.

Where the bedding of rocks is horizontal, or nearly
so, the surface will be much more flat and spreading
than where the dip is sharp, a condition which will
produce a rugged and rapidly- alternating landscape.
This fact is well worthy of notice, because we may
reason conversely that if a country be flat, the local
beds are tolerably level, and extend some distance in
any direction ; but if it be much broken, that they
rapidly disappear, having a high angle of inclination.
Upon the dip other properties of the beds depend ;
and it will be seen that it affects both directly and
indirectly the works constructed on their outcrop. The
relative elevation of varying deposits bears directly
upon the flow of surface water from, one area to
another ; therefore it affects the land springs, and in
the same degree the dryness or dampness of auy given
locality. The question of relative permeability is more
extensive and intricate, and upon this depend the all-
important points of the power of absorption of water
by the beds, and the nature and origin of deep-seated
springs. These points influence not merely the supply
to Artesian wells, but the liability to landslips, and
must be considered also in calculating the varying
pressures by which engineering works are especially
affected.

The phenomena of deep-seated springs, just referred



GEOLOGICAL STRATA. 15

to, depend not altogether upon permeability although
this is one of the chief elements in their production
but also upon the relative position of pervious and im-
pervious strata. These may succeed each other in the
simplest way, by being in regular sequence, with the
higher beds resting evenly upon the lower, each pos-


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