Marsh — Jurassic Formation on the Atlantic Coast. 109 



I took it for granted, in my paper cited, that American 

 geologists who were not familiar personally with the great 

 development of the Jurassic formation in Europe, or who had 

 had no opportunity of examining typical sections of this for- 

 mation in western America, or of seeing its deposits in place 

 full of characteristic fossils and extending hundreds of miles 

 in half a dozen states, were at least sufficiently acquainted 

 with the literature of the last twenty years to know that two 

 of the best-marked Jurassic horizons in any part of the world 

 existed in this country. 



Although my communication, as printed, was in fairly clear 

 English, I find it was misunderstood in various other points, 

 as subsequent reviews soon showed. If these marks of disap- 

 proval had been recorded by fireside geologists, who so often 

 differ with those who furnish facts, I should have followed my 

 usual rule and made no reply. They were, however, mainly 

 written by field geologists who had seen something of the 

 West, and ought evidently to have seen more, for the facts I 

 stated can be readily verified at any of the localities mentioned 

 and at many others. The failure to do so well illustrates a 

 law of human nature ; namely, that men see what they have 

 eyes to see. The West is an extensive country. The plant 

 men who go there seem to see only fossil plants ; the inverte- 

 brate collectors notice only their own favorites, and as both 

 classes are numerous, the extinct vertebrates are too often 

 overlooked or only peculiar and striking specimens secured. 

 Thus the most valuable evidence as to the age of strata is 

 neglected, and the decision rendered has so frequently to be 

 reversed. This neglect is not confined to field work alone, 

 where fossil vertebrates should be found, but too often extends 

 to the literature of the subject. 



Let me illustrate this by a short quotation from a well-known 

 work : 



" The Jurassic system, which is so largely developed in Europe, 

 containing the remains of huge swimming and flying reptiles * * 

 is but sparingly represented in American geology, and none of 

 the gigantic vertebrates have as yet been found here."* 



The above extract may fairly be taken as representing the 

 information on the subject known to the authors, or at least to 

 the editor, when this work was published. It is, moreover, a 

 fair sample of much that has since been written about the Juras- 

 sic formation of this country and its fossil contents, especially 

 by those not familiar with this subject, but whose work in 

 allied fields should at least have made them acquainted with 

 the main results of our vertebrate paleontology, which had 

 become a part of the world's scientific knowledge. 



* Geology of the Black Hills, by Newton and Jenney; edited by G. K. Gilbert: 

 p. 151,1880. 



