June 10, 1910] 



SCIENCE 



911 



these changes is justified, and in the second 

 place, whether they are likely to be accepted. 

 Like other innovations, these will have to be 

 tried out by the test of time and usage. It 

 may be suggested in this connection that, if 

 the Cambrian and Ordovician are to be 

 bracketed as an era, the Pennsylvanian and 

 Permian should also be set off by themselves 

 for reasons which are well brought out by Mr. 

 Schuchert's own discussion of these periods. 

 To the reviewer it appears even more just that 

 the Mesozoic era should be divided into two, 

 the line of separation being marked by the 

 intense and widespread Sierran disturbance. 

 To be consistent in having periods based on 

 ■diastrophic movements, the author should also 

 combine the late Devonian with the Missis- 

 sippian as one period, — a procedure which is 

 sanctioned in effect on page 493, where it is 

 «aid "... the diastrophism at the conclusion 

 of the Devonic does not appear to have been 

 marked in character. ... In this instance the 

 life record is thought to have greater value 

 than the physical one in separating the 

 Devonic from the Mississippic, but should the 

 principle of diastrophism be the sole guide, 

 then these two periods seemingly must be 

 ■combined into one." 



A study of the paper brings out the fact 

 that the author has worked largely from the 

 point of view of the paleontologist, excluding 

 in large measure the data of other sides of 

 geology. Indeed, this may be inferred 

 directly from the author's own paragraphs on 

 methods. On page 525 it is remarked that 

 " these maps . . . are still inadequate, as far 

 as presenting a final . . . geographic distribu- 

 tion of the various faunas is concerned." In 

 other words the maps are really faunal maps 

 rather than strictly geographic. That is to 

 say, they show the distribution of fossils 

 rather than of land and sea. Perhaps the 

 author will contend that these are one and 

 the same, but it is quite certain that others 

 wiU dissent from this view and with much to 

 be said on their side. In the reviewer's judg- 

 ment, valuable information can be drawn 

 from certain sources of which Mr. Schuchert 

 appears to have availed himself only in small 



measure, namely, the character and changes 

 in the structure and composition of the sedi- 

 ments and the relations of conformity and 

 unconformity between them. For example, 

 the author excludes the interior sea from the 

 Utah-Montana region at various times in the 

 Paleozoic era, because the necessary faunas 

 have not been found; in the face, however, of 

 the fact that in many places an unbroken 

 Sequence of marine deposits has been found 

 ranging from middle Cambrian to Mississip- 

 pian. Many stratigraphers will not agree that 

 the failure to find a fauna in a given section 

 proves the existence of a " break " or " strati- 

 graphic hiatus," much less a " disconformity." 

 If the section is completely exposed and if 

 there is no physical evidence of an unconform- 

 ity it would seem that the burden of proof 

 rests upon any one who doubts that sedimen- 

 tation was continuous during the periods in 

 question, whether or not the faunas are pres- 

 ent. 



A reading of the paper gives the impression 

 that the author recognizes only two important 

 factors which cause differences in faunas, i. e., 

 time and geographic isolation ; in other words, 

 that the Cambrian and Ordovician faunas of 

 New York are unlike because one is much 

 later than the other, while the Cambrian 

 faunas of New York and Utah are dissimilar 

 because they lived in marine provinces be- 

 tween which migration was impossible. It is 

 occasionally admitted in the paper, however, 

 and is generally recognized by biologists, that 

 a third factor is operative — the environ- 

 mental or edaphic factor. That the author is 

 aware of this is indicated by the statement on 

 page 589 : " The wide difference between the 

 Cretacic of Mexico and that of the United 

 States may be due in part to the decided 

 limestone facies of the former region. . . ." 

 But in most other instances where this factor 

 might well come into play it seems to have 

 been left out of consideration. Thus on page 

 550 it is remarked that the "wonderful 

 Burlington crinoid fauna " is unknown " in 

 the western sea." Since crinoids prefer cer- 

 tain environmental conditions and have by no 

 means a uniform distribution on the modem 



