150 



SCIENCE. 



[N. S. Vol. VIII. No. 188. 



haps find the information he needs in text- 

 books. 



First of all, however, I must question 

 the accuracy of some of the statements in 

 his review of my paper. One of these is 

 as follows : 



" Through a comparison of vertebrates 

 from the Potomac formation with verte- 

 brates from other formations he has in- 

 ferred the Jurassic age of the Potomac , 

 but he gives no hint of the character of his 

 evidence or the course of his reasoning."* 



Had this critic read the whole of my 

 paper he would have found the following 

 statement bearing on this point : 



" The Jurassic age of the Atlantosauras 

 beds of the West has now been demon- 

 strated beyond question by the presence of 

 a rich fauna of mammals, birds, reptiles 

 and fishes. Among these, the Sauropoda 

 were dominant, and the other Dinosaurs 

 well represented . 



"In the Potomac beds of Maryland the 

 same Jurassic vertebrate fauna is present, 

 as shown by the remains of five different 

 orders of reptiles already discovered in 

 them. Among the Dinosaurs are the Sau- 

 ropoda, the Theropoda and the Predentata, 

 the first group repi-esented by several genera 

 and a great number of individuals. One 

 of these genera is Pleurocmlus, which has 

 also been found in the Jurassic of the West. 

 Besides the Dinosaurs, characteristic re- 

 mains of Croeodilia and Tedudinata are not 

 uncommon, and various Fishes have been 

 found. The remains of these six groups 

 already known ai-e amply sufiicient to de- 

 termine the age of the formation, and still 

 more important discoveries doubtless await 

 careful exploration. "f 



Mr. Gilbert's next statement, which is 

 also without real foundation, is as follows : 



" The conclusion that the Atlantosaurus 

 and other horizons of the Eocky Mountain 



* Science, Vol. IV., p. 876, 1896. 

 t Science, Vol. IV., p. 814, 1896. 



region are Jurassic was announced in the 

 same way, without citation of evidence." 



The announcement of the Atlantosaurus 

 beds as Jurassic was accompanied by a sec- 

 tion showing their exact position in the 

 geological scale, and the characteristic 

 genera of Eeptilia which then indicated 

 their Jurassic age.* This was followed by 

 descriptions, in rapid succession, of many 

 other vertebrate fossils, proving beyond 

 question that the horizon was Jurassic. 

 The Baptanodon beds were also defined, 

 and their position in the geological series 

 established by characteristic fossils. The 

 demonstration on this point I have already 

 given above and need not repeat here. 



Another point needs correction, as Mr. 

 Gilbert evidently consulted my recent clas- 

 sification of the Dinosauriaf without appre- 

 preciating the evidence it contained. This 

 is shown by the following quotation from 

 his review : 



" The closest aifinity of the European and 

 American formations seems to be expressed 

 by the statement that there is one American 

 genus which falls in the same family with 

 a European genus." 



The genera named in my recent classifi- 

 cation were mainly typical forms, and I had 

 no intention of making a complete cata- 

 logue of all the known genera, as anyone 

 familiar with the subject could readily see. 

 By way of further instruction, let me repeat 

 here what I have recently said about one of 

 these typical forms. 



" Pleuroccelus is one of the most character- 

 istic genera of the Sauropodous Dinosauria, 

 and its value in marking a geological hor- 

 izon should, therefore, have considerable 

 weight. It is now known from the two 

 European localities mentioned above, both 



"■'■Prooeediiigs of the American Association, Nashville 

 meeting, p. 220, 1878 ; see also Popular Science 

 Monthly, p. 520, March, 1878. 



fThe Dinosaurs of North America, 16th Annual 

 Report U. S. Geological Survey, p. 238, 1896. 



