The Principles of Stratigraphical Geology

The Principles of Stratigraphical Geology

Author:
J. E. Marr
Author:
J. E. Marr
Format:
epub
language:
English

%title插图%num
Author: Marr, J. E. (John Edward), 1857-1933
Geology
Stratigraphic
The Principles of Stratigraphical Geology
Cambridge Natural Science Manuals.
Geological Series.
THE PRINCIPLES
OF
STRATIGRAPHICAL GEOLOGY
London: C. J. CLAY AND SONS,
CAMBRIDGE UNIVERSITY PRESS WAREHOUSE,
AVE MARIA LANE.
AND
H. K. LEWIS,
136, GOWER STREET, W.C.

Leipzig: F. A. BROCKHAUS.
New York: THE MACMILLAN COMPANY.
Bombay: E. SEYMOUR HALE.

THE PRINCIPLES
OF
STRATIGRAPHICAL GEOLOGY

BY

J. E. MARR, M.A., F.R.S.

FELLOW AND LECTURER OF S. JOHN’S COLLEGE, CAMBRIDGE,
AND UNIVERSITY LECTURER IN GEOLOGY.
CAMBRIDGE:
AT THE UNIVERSITY PRESS.
1898

[All Rights reserved.]

Cambridge:
PRINTED BY J. & C. F. CLAY,
AT THE UNIVERSITY PRESS.
PREFACE.
The present work has been written in order that students may gain by its perusal some idea of the methods and scope of Stratigraphical Geology. I believe that this idea can be obtained most satisfactorily, if a large number of the details connected with the study of the stratified rocks are omitted, and I have accordingly given very brief accounts of the strata of the different Systems.
The work is intended for use in conjunction with any book which treats of the strata of the Geological Column at considerable length; some of these books are mentioned on pages 124, 125.
J. E. M.
Cambridge,
November, 1898.
CONTENTS.

PAGE
CHAPTER I.
Introduction 1
CHAPTER II.
Account of the growth and progress of stratigraphical geology 6
CHAPTER III.
Nature of the stratified rocks 21
CHAPTER IV.
The law of superposition 31
CHAPTER V.
The test of included organisms 40
CHAPTER VI.
Methods of classification of the strata 58
CHAPTER VII.
Simulation of structures 72
CHAPTER VIII.
Geological maps and sections 84
CHAPTER IX.
Evidences of conditions under which strata were formed 97
CHAPTER X.
Evidences of conditions under which strata were formed, continued 116
CHAPTER XI.
The classification of the stratified rocks 125
CHAPTER XII.
The Precambrian rocks 132
CHAPTER XIII.
Cycles of change in the British area 149
CHAPTER XIV.
The Cambrian system 152
CHAPTER XV.
The Ordovician system 164
CHAPTER XVI.
The Silurian system and the changes which occurred in Britain at the close of Silurian times 174
CHAPTER XVII.
The Devonian system 183
CHAPTER XVIII.
The Carboniferous system 192
CHAPTER XIX.
The changes which occurred during the third continental period in Britain; and the foreign Permo-Carboniferous rocks 202
CHAPTER XX.
The Permian system 209
CHAPTER XXI.
The Triassic system 218
CHAPTER XXII.
The Jurassic system 226
CHAPTER XXIII.
The Cretaceous system 236
CHAPTER XXIV.
The Eocene rocks 244
CHAPTER XXV.
The Oligocene and Miocene periods 251
CHAPTER XXVI.
The Pliocene beds 256
CHAPTER XXVII.
The Pleistocene accumulations 260
CHAPTER XXVIII.
The Steppe period 267
CHAPTER XXIX.
The Forest period 275
CHAPTER XXX.
Remarks on various questions 278

ADDENDA ET CORRIGENDA.

p. 38, line 15 from bottom: for ‘joining’ read ‘jointing’
p. 208, line 6 from bottom: for ‘Dr’ read ‘Messrs Medlicott and’
p. 214, line 15 from bottom: after ‘Permo-Carboniferous Strata’ insert ‘through the Permian’
p. 217, last line of footnote: for ‘Dr’ read ‘Messrs Medlicott and’
p. 217, insert a second footnote: ‘For information concerning the Permian volcanic rocks see Sir A. Geikie’s Ancient Volcanoes of Great Britain.’
p. 235, insert a footnote: ‘A good account of the British Jurassic rocks will be found in Mr H. B. Woodward’s Memoir on “The Jurassic Rocks of Britain.” Mem. Geol. Survey, 1893—.’
p. 250, top line: for ‘Gardiner’ read ‘Gardner’

[Trancriber’s Note: Above corrections were made to the text.]


CHAPTER I.
INTRODUCTION.
It is the aim of the Stratigraphical Geologist to record the events which have occurred during the existence of the earth in the order in which they have taken place. He tries to restore the physical geography of each period of the past, and in this way to write a connected history of the earth. His methods are in a general way similar to those of the ethnologist, the archæologist, and the historian, and he is confronted with difficulties resembling those which attend the researches of the students of human history. Foremost amongst these difficulties is that due to the imperfection of the geological record, but similar difficulty is felt by those who pursue the study of other uncertain sciences, and whilst this imperfection is very patent to the geologist, it is perhaps unduly exaggerated by those who have only a general knowledge of the principles and aims of geology.
The history of the earth, like other histories, is a connected one, in which one period is linked on to the next. This was not always supposed to be the case; the catastrophic geologist of bygone times believed that after each great geological period a convulsion of nature left the earth’s crust as a tabula rasa on which a new set of records was engraved, having no connexion with those which had been destroyed. Careful study of the records of the rocks has proved that the conclusions of the catastrophists were erroneous, and that the events of one period produce their impression upon the history of the next. Every event which occurs, however insignificant, introduces a new complication into the conditions of the earth, and accordingly those conditions are never quite the same. Although the changes were no doubt very slow, so that the same general conditions may be traced as existent during two successive periods, minor complications occurred in the inorganic and organic worlds, and we never get an exact recurrence of events. Vegetable deposits may now be in process of accumulation which in ages to come may be converted into coal, but the general conditions which were prevalent during that Carboniferous period when most of our workable coal was deposited do not now exist, and will never exist again. The changes which have taken place and which are taking place show an advance from the simple to the more complex, and the stratigraphical geologist is confronted with a problem to which the key is development, and it is his task to trace the development of the earth from the primitive state to the complex condition in which we find it at the present day.
Our general ignorance of the events of the earliest periods of the history of the earth will be emphasised in the sequel, and it will be found that the complexity which marks the inorganic and organic conditions which existed during the deposition of the earliest rocks of which we have detailed knowledge points to the lapse of enormous periods of time subsequent to the formation of the earth, and previous to the deposition of those rocks. The imperfection of the record is most pronounced for that long period of time, but in this respect the geologist is in the same condition as the student of human history, for the relics of the early stone age prove that man in that age had attained a fairly high state of civilisation, and the gap which separates palæolithic man from the first of our race is relatively speaking as great as that which divides the Cambrian period from the commencement of earth-history. Nevertheless, human history is a science which has made gigantic strides towards the solution of many problems connected with the development of man and civilisation, and similarly geology has advanced some way in its task of elucidating the history of our globe.
The task of the stratigraphical geologist is two-fold. In the first place, he must establish the order of succession of the strata, for a correct chronology is of paramount importance to the student of earth-lore. The precautions which must be taken in making out the order of deposition of the rocks of any area, and correlating those of one area with those of another will be considered in the body of the work. When this task is completed, there yet remains the careful examination of all the information supplied by a study of the rocks of the crust, in order to ascertain the actual conditions which existed during the deposition of any stratum or group of strata. In practice, it is generally very difficult to separate these two departments of the labour of the stratigraphical geologist, and the two kinds of work are often done to a large extent simultaneously, or sometimes alternately. Frequently the general succession of the deposits comprising an important group is ascertained, and at the same time observations made concerning the physical characters of the deposits and the nature of their included organisms, which are sufficient to afford some insight into the general history of the period when these deposits were laid down; a more detailed classification of the same set of deposits may be subsequently made, and as the result of this, more minute observations as to the variations in the physical and biological conditions of the period are possible, which permit us to write a much more concise history of the period. So great has been the tendency to carry on work in a more and more detailed manner, that it is very difficult if not impossible to tell when any approach to finality is reached in the study of a group of strata in any area. Roughly speaking, we may state that our knowledge of a group of strata is obtained by three processes, or rather modifications of one process. The general order of succession is established by the pioneer, frequently as the result of work carried on through one or two seasons. Subsequently to this, a more minute subdivision of the rocks is possible as the result of labours conducted by one or more workers who are enabled to avail themselves of the work of the pioneer, and our knowledge of the rocks is largely increased thereby. But the minutiæ, often of prime importance, are supplied by workers who must spend a large portion of their time in the area where the work lies, and it is only in districts where work of this character has been performed, that our knowledge of the strata approaches completion. The strata of the Arctic regions, for example, have in many places been examined by pioneers, but a great deal remains to be done in those regions; the main subdivisions only have been defined in many cases, and our information concerning the physical history of Arctic regions in past times is comparatively meagre. To come nearer home—a few miles north of Cambridge lies the little patch of Corallian rock at Upware; it has been frequently visited, and a large suite of organic remains extracted from it, but no one has devoted the time to the collection of remains from this deposit which has been devoted to that of some other formations presently to be mentioned, and accordingly our knowledge of the fauna of that deposit is far from complete. Contrast with this the information we possess of the little seam known as the Cambridge Greensand, from which organic remains have been sedulously collected during the extensive operations which have been carried on for the extraction of the phosphatic nodules which occur in the seam. The suite of relics of the organisms of that period is accordingly far more perfect than in the case of many other beds, and indeed the large and varied collection of relics of the vertebrata of the period which furnish much information of value to the palæontologist would not have been gathered together, had not this seam been so carefully worked, and an important paragraph in the chapter bearing on the history of this period would have remained unknown to us. Again, two little patches of limestone of the same age, one in central England and the other in the island of Gothland, have been the objects of sedulous inquiry by local observers, and we find again that our knowledge of the physical history of the period, as regards these two regions, is exceptionally perfect. Special stress is laid upon this point, for in these days, when every county possesses its learned societies whose members are desirous of advancing in every possible way the progress of science, it is well to insist upon the importance of this detailed work which can only be done by those who have a large amount of time to devote to the rigorous examination of the rocks of a limited area.


CHAPTER II.
ACCOUNT OF THE GROWTH AND PROGRESS OF STRATIGRAPHICAL GEOLOGY.
The history of the growth of a science is not always treated as an essential part of our knowledge of that science, and many text-books barely allude to the past progress of the science with which they deal. The importance of a review of past progress has, however, attracted the attention of many geologists, and Sir Charles Lyell, in his Principles of Geology, gave prominence to an historical sketch of the rise and progress of the science. Historical studies of this nature have more than an academic value; the very errors made by men in past times are useful as warnings to prevent those of the present day from going astray; the lines along which a science has progressed in the past may often be used as guides to indicate how work is to be conducted in the future; but perhaps the greatest lesson which is taught by a careful consideration of the rise and progress of a study is one which has a moral value, for he who pays attention to the growth of his science in past times, gains a reverence for the old masters, and at the same time learns that a slavish regard for authority is a dangerous thing. This is a lesson which is of the utmost importance to the student who wishes to advance his science, and will prevent him from paying too little attention to the work of those who have gone before him, whilst it will enable him to perceive that as great men have fallen into error through not having sufficient data at their disposal, he need not be unduly troubled should he find that conclusions which he has lawfully attained after consideration of evidence unknown to his predecessors clash with those which they adopted. Want of this historic knowledge has no doubt caused many workers to waste their time on work which has already been performed, but it has also led others to withhold important conclusions from their fellow-workers because they were supposed to be heterodox. In an uncertain science like geology one of the great difficulties is to keep an even balance between contempt and undue respect for authority, and assuredly a scientific study of the past history of a science will do much to enable a student to attain this end. It will be useful, therefore, at this point to give a brief account of the rise and progress of the study of stratigraphical geology, so far as that can be done without entering into technical details, at the same time recommending the student to survey the progress of this branch of our science for himself, after he has mastered the principles of the subject, and such details as are the property of all who have studied the science from the various text-books written for advanced students.
William Smith, the ‘Father of English Geology,’ is rightly regarded as the founder of stratigraphical geology on a true scientific basis, but like all great discoverers, his work was foreshadowed by others, though so dimly, that this does not and cannot detract from his fame. It is desirable, however, to begin our historical review at a time somewhat further back than that at which Smith gave to the world his epoch-making map and memoirs.
Before the eighteenth century, stratigraphical geology cannot be said to have existed as a branch of science—the way had not been prepared for it. Data had been accumulated which would have been invaluable if at the disposal of open-minded philosophers, but with few exceptions prejudice prevented the truth from becoming known. There were two great stumbling-blocks to the establishment of a definite system of stratigraphical geology by the writers of the Middl

Download This eBook
This book is available for free download!

评论

普人特福的博客cnzz&51la for wordpress,cnzz for wordpress,51la for wordpress
The Principles of Stratigraphical Geology
Free Download
Free Book