LAHAM1E FORMATION. 29 



are generally divisible into three benches by clay bands or coal scams, 

 and it is within these sandstones that the best workable coals are found. 

 Coal seams have also been found in the upper clayey division, but the 

 coals are lignites with higher percentages of water and of inferior economic 

 value. One band of sandstone above the two lower benches is of impor- 

 tance as being more generally fossiliferous, and hence a valuable indicator 

 in searching for coal. It contains a considerable percentage of lime. The 

 fossils found are mollusks of brackish- and fresh-water habit, together with 

 remains of plants. No vertebrates have yet been found in beds that could 

 with certainty be assigned to the Laramie horizon, as defined in this report. 



POST-LARAMIE MOVEMENT. 



At the close of the Laramie period the general shallowing of the ocean 

 waters, which had been going on slowly during the latter part of Creta- 

 ceous time and which was probably accompanied by some elevation of the 

 sea-bottom, culminated in a widespread orographic movement whose effects 

 have been traced from one end of the continent to the other, hut are most 

 marked in the Cordilleran region. It is to this movement that the rough- 

 ing out and outlining of the mountain forms of the present Rocky Moun- 

 tain system has been generally ascribed, and while it is not possible to 

 decipher with certainty in a given region the amount of deformation which 

 was due to each of the orographic movements to which it has been sub- 

 jected, it is evident that the post-Laramie movement must have played 

 relatively the most important part in these deformations, since its results 

 were to shut out the ocean waters from the plain as well as from the 

 mountain areas of the entire Western region. 



In this post-Laramie movement not only was there a general conti- 

 nental elevation of the whole region, but the mountain areas suffered a 

 differential uplift in relation to the surrounding plains or lowlands, so that 

 the edges of the strata resting against these Hanks were in many places 

 upturned at considerable angles. With the dynamic movements which 

 caused the differential elevation of the mountain masses and which pro- 

 duced folding and dislocation of the strata was associated considerable 

 eruptive activity, which inaugurated a succession of outbreaks of eruptive 



