﻿190 FOSSIL LEAVES. July, 



water, and is frozen into a compact, hard rock, for 

 most of the year ; but becomes moist, and breaks 

 down under the influence of the hot rays of the 

 sun in spring. 



Potter's clay^ of a grey or brown colour, al- 

 ternates with the beds already named, in layers 

 varying from one foot to forty or more in thick- 

 ness. This clay is often highly bituminous, and is 

 penetrated by ramifications of carbonaceous matter, 

 resembling the roots of vegetables. About ten miles 

 above Great Bear River, a layer of this material, 

 lying immediately over a bed of coal which was on 

 fire, has been baked so as to resemble a fine yel- 

 lowish-coloured biscuit porcelain. In a part of 

 this, I found numerous impressions of leaves, most 

 of them dicotyledonous, but one of them apparently 

 coniferous, and belonging, probably, to the yew 

 genus. The existence on many of the leaves of 

 the latter plant of little round bodies like the 

 fructification of ferns, invested the specimens 

 with much interest: and I am indebted to Mr. 

 Brown for examining them, and superintending 

 the accurate drawings, made by Mr. Sowerby, 

 junior, from which the accompanying plates 

 have been engraved. The clay had unfortunately 

 cracked so much under the influence of the heat to 

 which it had been subjected, that I could not obtain 

 entire specimens of the larger dicotyledonous leaves, 



