3i W. Cross — Post- Laramie Deposits of Colorado. 



bearing of fossil plants in determining the age of the Denver 

 and allied deposits is useless. 



The few invertebrate fossils found in the Denver beds are, 

 according to Dr. C. A. White," of no special value in the 

 present case. Yivvparus trochiformis and Goniobasis tenui- 

 carinata are the only specifically identifiable forms as yet 

 known, while imperfect forms referable to Corbictda, Physa, 

 and Unio accompany them. 



The vertebrate fauna known from the Denver and Arapa- 

 hoe beds is small, but its character is such as to raise some very 

 broad questions for settlement before its value for purposes of 

 detailed correlation can be determined. At the time the Den- 

 ver and Arapahoe formations were described a considerable 

 number of fossil bones had been found, and since that time 

 additional material has been obtained by Mr. G. L. Cannon, Jr. 

 All the material collected has been examined by Professor O. 

 C Marsh, who identifies fragments of turtles, crocodiles, and 

 dinosaurs.f Only the latter are of especially recognized im- 

 portance in this case. They belong for the most part to the 

 remarkable new family, the Ceratopsidte. of which so many 

 wonderful forms have been described within the last three 

 years, and it is necessary at this point to pass in review certain 

 phases of the discoveries made by Professor Marsh, and the 

 facts stated in the publications concerning them. 



In a series of articles in the American Journal of Science 

 beginning December, 1888, Prof. Marsh has described a won- 

 derful new fauna said to occur in the Laramie of Montana, 

 Wyoming and Colorado, the two most important elements of 

 which are a group of horned Dinosaurs forming a new sub- 

 order, the Ceratopsia, and a large number of small mammals. 

 The new Dinosaurs are closely related to Stegosaurus in many 

 features of the skeleton, but the skull and dermal armor have 

 become strangely modified and possess marked characteristics 

 " not before seen in the Dinosauria." With the exception of 

 a few isolated bones and teeth mentioned by Cope the mam- 

 malian fauna associated with these Dinosaurs is the first to be 

 discovered in the American Cretaceous, and is closely allied to 

 that known in the Jura, and widely different from that charac- 

 terizing the Wasatch Eocene.;}: 



* Cited in article describing the Denver Formation, this Journal, vol. xxxvii, p. 

 275. 



f The fossil from the Denver beds originally described by Professor Marsh as 

 Bison alticornis is now regarded by him as belonging to Ceratops (this Journal, 

 xxxviii, 174, 1889). 



\ The writer wishes to acknowledge the courtesy and kindness of Professor 

 Marsh in showing him a large number of the remarkable and important forms 

 which have been found in the Ceratops beds, and in explaining the great prob- 

 lems they present to the evolutionist, together with their apparent bearing upon 

 questions of historical geology.- ■ 



