EAYDEx.] GEOLOGY COAL STRATA. 27 



Laramie Plains aud Colorado with the vast group in the Northwest. I 

 have traced this geographical connection step by step over this great 

 area, have studied the formation with some care, and collected both 

 vegetable and animal fossils in the greatest abundance from point to 

 jioint. I woald say, however, that comparatively few of the fresh-water 

 species of Mollusca, so abundant in the i^orthwest, are found either in 

 Colorado or the Laramie Plains; but it possesses the same character, 

 and many of the same species of plants are scattered all over this im- 

 mense area. 



