496 



NA TURE 



[Septemri:r 24, 1896 



the magnificent fauna of the Wenlock limestone would have 

 been far less perfectly known than it is, if it were not for the 

 collections of men like the late Colonel Klelclier and ihe late Dr. 

 Orindrod. Again, the existence of the rich fauna i)f the Cam- 

 bridge Greensand would have been unsuspected had not the bed 

 known by that name been worked for the phosphalic nodules 

 which it contains. 



It is very desirable that large collections of varieties of species 

 should be made, for in this matter the record is very imperfect. 

 There has been, and, I fear, is still, a tendency to reject speci- 

 mens when their characters do not conform with those given in 

 specific descriptions, and thus much valuable material is lost. 

 .Local observers should be specially careful to search for varieties, 

 which may be very abundant in places where the conditions 

 were favourable for their production, though rare or unknown 

 elsewhere. Thus, I find the late Mr. W. Keeping remarking 

 that " it is noteworthy that at Upware, and indeed all other 

 places known to me, the species of Brachiofoda [of the A'eocoinian 

 beds] maintain much more distinctness and isolation from one 

 ■irnother than at Brickhill."' The latter place appears to be one 

 where conditions were exceptionally favourable in Neocomian 

 .times for the production o( intermediate forms. 



A mere knowledge of varieties is, however, of no great use 

 to the collector without a general acquaintance with the mor- 

 ]5hology of the organisms whose remains he extracts from the 

 earth's strata, and one who has this can do signal service to 

 the science. It is specially important that local observers should 

 iie willing to devote themselves to the study of particular groups 

 ■of organisms, and to collect large suites of specimens of the 

 ^roup they have chosen for study. With a group like the 

 graptolites, for instance, the specimens which are apparently 

 best preserved are often of little value from a morphological 

 point of view, and fragments frequently furnish more information 

 ■than more complete specimens. These fragments seldom find 

 their way to our museums, and accordingly we may examine a 

 large suite of graptolites in those museums without finding any 

 e.^;amples showing particular structures of importance, such as 

 the sac-like bodies carried by many of these creatures. As an 

 illustration of the value of work done by one who has made a 

 special study of a particular group of organisms, I may refer to 

 the remarkable success achieved by the late Mr. Norman Glass 

 in developing the calcareous supports of the brachial processes 

 ■of Brachiopods. Work of this character will greatly reduce the 

 imperfection of the record from the biologists' point of view. 



The importance of detailed work leads one to comment upon 

 the general methods of research which have been largely adopted 

 in the case of the stratified rocks. The principle that strata are 

 identifiable by their included organisms is the basis of modern 

 work, as it was of that which was achieved by the father of 

 English Geology, and the identification of strata in this manner 

 has of recent years been carried out in very great detail, 

 notwithstanding the attempt on the part of some well-known 

 writers to show that correlation of strata in great detail is 

 impossible. The objection to this detailed work is mainly 

 founded upon the fact that it must take time for an 

 organism or group of organisms to migrate from one area to 

 another, and therefore it was stated that they cannot have lived 

 contemporaneously in two remote areas. But the force of this 

 objection is practically done away with if it can be shown that 

 .the time taken for migration is exceedingly short as compared 

 ivith the time of duration of an organism or group of organisms 

 upon the earth, and this has been shown in the only possible 

 way — namely, by accumulating a very great amount of evidence 

 as the result of observation. The eminent writers referred to 

 above, who were not trained geologists, never properly grasped 

 the vast periods of time which must have elapsed during the 

 • occurrence of the events which it is the geologist's province to 

 study. An historian would speak of events which began at 

 noon on a certain day and ended at midnight at the close of 

 that day as contemporaneous with events which commenced 

 and ended five minutes later, and this is quite on a par with 

 what the geologist does when correlating strata. Nevertheless, 

 .there are many people who .still view the task of correlating 

 minute .subdivisions of stratified systems with one another, with 

 a certain amount of suspicion, ii not with positive antipathy ; 

 but the work must be done for all that. Brilliant generalisations 

 are attractive as well as valuable, but the steady accumulation 



* W. Keeping, Sedgwick Essay: "The Fossils and Pala:ontu!ogical 

 Afiiniues of the Neocomian Deposits of Upware and Urickhill. " (Cam- 

 bridge, 1883.) 



NO. 1404, VOL. 54] 



of facts is as necessary for the advancement of the science as it 

 was in the days when the Geological Society was founded, and 

 its members applied themselves "to multiply and record 

 observations, and patiently to await the result at some future 

 period." I have already suggested a resemblance between 

 geology and cricket, and I may be permitted to point out that 

 just as in the game the free-hitter wins the applause, though the 

 patient " stone-waller" often wins the match, .so, in the science, 

 the man apt at brilliant generalisations gains the approval of the 

 general public, but the patient recorder of apparently insigni- 

 ficant details adds matter of permanent value to the stores of our 

 knowledge. In the case of stratigraphical geology, if we were 

 compelled to be content with correlation of systems only, and 

 were unable to ascertain which of the smaller series and stages 

 were contemporaneous, but could only speak of these as 

 " homotaxial," we should be in much the .same position as the 

 would-be antiquary who was content to consider objects 

 fashioned by the Romans as contemporaneous with those ot 

 medieval times. Under such circumstances geology would 

 indeed be an uncertain science, and we should labour in the 

 field, knowing that a satisfactory earth-history would never be 

 written. Let us hope that a brighter future is in store for us, 

 and let me urge my countrymen to continue to study the minute 

 subdivisions of the strata, lest they be left behind by the 

 geologists of other countries, to whom the necessity for this kind 

 of study is apparent, and who are carrying it on with great 

 success. 



The value of detailed work on the part of the stratigraphical 

 geologist is best grasped if we consider the recent advance that 

 has been made in our science owing to the more or less 

 exhaustive survey of the strata of various areas, and the applica- 

 tion of the results obtained to the elucidation of earth's history. 

 A review of this nature will enable us not only to see what has 

 been done, but also to detect lines of inquiry which it will be 

 useful to pursue in the future ; but it is obvious that the subject 

 is so wide that little more can be attem|)ted than to touch 

 lightly upon some of the more prominent questions. .A work 

 might well be written treating of the matters which I propose to 

 notice. We have all read our " Principles of Geology," or 

 "The Modern Changes of the Earth and its Inhabitants con- 

 sidered as illustrative of Geology," to quote the alternative title ; 

 some day we may have a book written about the ancient 

 changes of the earth and its inhabitants considered as illustrative 

 of geography. 



Commencing with a glance at the light thrown on inorganic 

 changes by a detailed examination of the strata, I may briefly 

 allude to advances wliich have recently been made in the study 

 of denudation. The minor faults, which can only be detected 

 when the small subdivisions of rock-groups are followed out 

 carefully on the ground, have been shown to be of great 

 importance in defining the direction in which the agents of 

 denudation have operated, as demonstrated by Prof. W. C. 

 Brfigger, for instance, in the case of the Christiania Fjord 

 (Nyt. Mag. for Natm-t'idfiisk., vol. xxx. (1886), p. 79); and I 

 have recently endeavoured to prove that certain valleys in the 

 English Lake District have been determined by shattered belts 

 of country, the existence of which is shown by following thin 

 bands of strata along their outcrop. The importance of the 

 study of the strata in connection with the genesis and subsequent 

 changes of river-systems is admirably brought out in Prof. W. 

 M. Davis's paper on "The Development of certain English 

 Rivers (Gciv^rafh. Joiiru., vol. v. (1895) P- '-7). a paper which 

 should be read by all physical geologists : it is, indeed, a 

 starting-point of kindred work which remains especially for 

 local observers to accomplish. Study of this kind not only adds 

 to our knowledge of the work of geological agencies, but helps 

 to diminish the imperfection of the record, for the nature ot 

 river-systems, when rightly understood, enaliles us to detect the 

 fqrmer presence of deposits over areas from w'hich they have 

 long since been removed by denudation. 



An intimate acquaintance with the lithological characters of 

 the strata of a district aftords valuable information in connection 

 with the subject of glacial denudation. The direction of glacial 

 transport over the British Isles has been largely inferred from a 

 study of the distribution of boulders of igneous rock, whilst 

 those of sedimentary rock have been less carefully observed. 

 The importance of the latter is well shown by the work which 

 has been done in Northern Europe in tracing the .Scandinavian 

 boulders to their sources, a task which could not have been 

 performed successfully if the Scandinavian strata had not been 



