NATURE 



585 



THURSDAY, OCTOBER 21, 1897. 



GEOLOGY FROM AN AMERICAN POINT 

 OF VIEW. 

 An Introduction to Geology. By William B. Scott, Blair 

 Professor of Geology and Palaeontology in Princeton 

 University. Pp. xxvii + 573. 8vo. (New York : The 

 Macmillan Company, 1897.) 



IT is always well to keep in touch with the methods and 

 conclusions of workers in other countries ; and in a 

 general way this can only be done by text-books. In this 

 respect the present work will be found of considerable ser- 

 vice to British students of geology. It is intended especi- 

 ally for .American students, and has been written both for 

 those who desire to pursue the subject exhaustively, and 

 for those who seek only to learn the principal results of 

 the science. To satisfy the needs of these different classes 

 is a task that it would be impossible fully to attain in any 

 work, for the details required by some would be apt to 

 repel others. Nevertheless, the author has well succeeded 

 in his main endeavours. 



We may pass over that usual stumbling-block to the 

 general reader, the chapter on rock-forming minerals, 

 which, as the author says, " is intended rather for refer- 

 ence than for actual learning." It might perhaps have 

 found place in the appendix, alongside the table of 

 European strata and the classification of animals and 

 plants. It is essential, however, that something be said 

 on the subject, and the author treats it concisely and 

 without needless detail. He then proceeds to give a 

 full and very interesting account of the changes which 

 are now in progress on the surface of the earth, admirably 

 illustrated with photographic reproductions, and embody- 

 ing the results of the most recent researches. 



The igneous and stratified rocks, their structure and 

 dislocations, are next described in a similar manner, 

 with photographic and diagrammatic illustrations; and 

 of much interest to British students is the account of 

 various kinds of folds and displacements to which 

 American geologists in particular have assigned special 

 names. 



In the part relating to physiographical geology again 

 we have very useful illustrations of many phenomena 

 and of terms now largely used in geological literature, 

 but not as yet so clearly explained in other text-books. 

 The chapter on the adjustment of rivers, dealing with ante- 

 cedent and superimposed rivers and subsequent streams, 

 as explained by Prof. W. M. Davis, cannot fail to be 

 of service. The treatment of the many subjects causes 

 here and there some repetition, as in the case of soil 

 <pp. 76, 124, and 217), and a little condensation might be 

 made in a future edition in reference to this and a few 

 other matters. 



The least satisfactory part of this volume is that 

 dealing with stratigraphical palaeontology. Something 

 should have been said about geological zones and of 

 their importance in correlating strata belonging to 

 distant regions. As it is, we have to be content with a 

 lithological account of the leading formations developed 

 in America, and of the extent of these in other parts of 

 the world ; we are told something about their method of 

 NO. T460. VOL. 56] 



formation, but as regards the life-history we have simply 

 a statement of the genera of Ordovician or Devonian, as 

 the case may be, and figures of some of the character- 

 istic American species. There is but a meagre hint that 

 rocks of Devonian and Old Red Sandstone type have 

 been recognised in America. We are informed that 

 along the eastern shore of the Chemung Sea (Upper 

 Devonian), there was accumulated an immensely thick 

 sandstone (7500 feet), which was formerly supposed to 

 represent a distinct series, and called the Catskill. 

 Again, it is stated that " the so-called Catskill of New 

 York is very like the Old Red, and contains similar 

 fossils." Surely it would have been of interest to state 

 that the rocks of this type in America contain Halo 

 ptychius and Bothriolepis. The lack of special palasonto- 

 logical information is felt when we read that " in North 

 America the passage from Silurian to the Devonian is 

 very gradual, the former drawing to its close without dis- 

 turbance ; and there is still some difference of view as to 

 just where the line between the two systems should be 

 drawn." Moreover, " in many parts of North America 

 the Devonian was followed so quietly by the Carbon- 

 iferous, that it is very difficult to draw the line between 

 them ; but in other regions notable geographical changes 

 occurred." These indications of a gradual passage are 

 so similar to those met with in this country, that a few 

 further materials for comparison would have been very 

 welcome. 



The author's general scheme of classification is a 

 happy one. He uses the term Archccan to include the 

 most ancient rocks, often spoken of as the " basement or 

 basal complex." Between this Archaean complex and 

 the Cambrian comes the Algonkian period, termed 

 Eozoic, though at present the indications of former life 

 are mainly inferred from the presence of limestones and 

 graphite. Above the Cambrian we have the Ordovican, 

 Silurian, and other periods. The Permian is grouped 

 with the Palaeozoic, as it is on the whole distinctly con- 

 nected with it, although '' it has several features which 

 mark it out as transitional to the Mesozoic." In follow- 

 ing through the account of the various formations wc 

 find many matters of considerable interest, and we are 

 also introduced to the various terms applied to sub- 

 divisions of the geological series in North America. 

 Among these the " Clear Fork Beds " of the Permian 

 and the " Goodnight Stage " of the Pliocene, sound 

 somewhat strange when compared with British terms. 



There was a time when Eskers and Kames were con- 

 sidered to be synonymous. American geologists have for 

 some time recognised a difference — Kames being con- 

 I sidered as " hillocks or short ridges of stratified drift, 

 formed by the deposition of materials from subglacial 

 ; streams as they escape from unJer the margin of the 

 ice," while Eskers or Asar are " long, winding ridges of 

 I sand and gravel," which follow the general direction of 

 I the moving ice, and may have been laid down in channels 

 ; or tunnels in the ice. These and other explanations are 

 j interesting and useful. In some instances the references 

 I are far too meagre, as in the case of Cherts, where their 

 I organic origin through sponge-spicula and radiolaria is 

 I not sufficiently indicated. 



The numerous photographic illustrations are very 

 I beautiful and instructive ; indeed, they lend additional 



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