118 KANSAS UNIVERSITY QUARTERLY. 



Tertiary rocks of the arid plains, these rocks have reached a high de- 

 gree of induration produced by this mode of deposition. 



PALEONTOLOGY. 



Jurassic. The Jurassic period was a period of exj)ansion for ma- 

 rine life. It was a period when, by the encroachment of the oceanic 

 waters, great epicontinental seas and bays were formed. At least 

 three of these bodies of water existed on the continent of Eurasia and 

 one upon the American continent, while there were less extensive en- 

 croachments on all the large land masses. These eijicontinental seas, 

 by furnishing additional feeding grounds, increased to a marked de- 

 gree the number of marine organisms. And in so far as these seas 

 restricted the land area they restricted also the development of ter- 

 restrial life.* 



During Ujjper Jurassic time three faunal stages marked the growth 

 of marine transgression upon the borders of the continents. These 

 stages are known in England as the Lower Oolyte, the Middle Oolyte, 

 and the Upper Oolyte. Only one of these three stages, the Upper 

 Oolyte, is represented in the Jura of the American interior province, 

 and jDrobably only the middle part of that. In other words, of the 

 three Upper Jurassic faunas recognized in the Pacific coast deposits 

 of California and in northern Eurasia, only one is recognized in the 

 Wyoming Jura. 



The discovery of beds of Jurassic age in the interior was first an- 

 nounced by Meek in 1858. f In correlating these beds with the Jura 

 of the old world, the writer says: "The organic remains found in 

 these series present, both individually and as a group, very close 

 afhnities to those in the Jurassic epoch in the old world ; so close, in- 

 deed, that in some instances, after the most careful comparisons with 

 figures and descriptions, we are left in doubt whether they should be 

 regarded as distinct species or as varieties of well-known European 

 Jurassic forms. Among those so very closely allied to foreign Juras- 

 sic species may be mentioned an ammonite we have described under 

 the name of A. cordifoTmis, which we now regard as probably iden- 

 tical with A. cordatus of Sowerby ; a gryphsea we have been only 

 able to distinguish as a variety from G. calceola Quenstedt; a pecten 

 scarcely distinguishable from /-*. lens Sowerby ; a modiola very closely 

 allied to M. cancellata of Goldf uss ; a belemnite agreeing very well 

 with B. excentricns." 



Since the publication of the above statements by Meek the paleon- 

 tology of the European Jura has been more completely worked out, 

 and some of the faunas, particularly that of northern Russia, are 



*For the principles involved in these statements see "A Systematic Source of Evolution of 

 Provincial Faunas," by T. C. Chamberlin. ( Jour. Geol., vol. VII, p. 597.) 



tGeological Report of the Exploration of the Yellowstone and Missouri Rivers. 



