154 



GEOLOGY. 



burning was relatively recent, and locally is still in progress. The firing 

 appears to have taken place on the sides of hills and valleys where 

 the lignite outcrops. Back from the slopes where the outcrops occur, 

 chimneys or vents appear to have sometimes developed, probably along 

 joints, leading up from the burning coal to the surface, giving rise to 

 " pseudo- volcanoes." The burning was accompanied by fusion, semi- 



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Fig. 397. — Map and section showing the position and relations of the several mem- 

 bers of the Cretaceous system, and the effect of a lava cap in the prevention o/ 

 erosion and in the development of mesas. Kp (Pierre formation) and Ktd (Trini- 

 dad formation), Montana series; Kl, Laramie series; Nb Neocene basalt. The sec- 

 tion is along the line AB of the map. (Hills, Elmoro, Colo., folio, U. S. Geol. Surv.) 



fusion, and baking, resulting in lava-like slag and brick-red banks of 

 indurated clay. The former has had, and is still having a notable 

 effect on the details of the topography developed by wind and water, 

 while the latter gives striking color to the landscape. Incipient meta- 

 morphism accompanied the heat developed by the combustion. 



Transition beds between Mesozoic and Cenozoic. — In general, the 

 Laramie is conformable with the Montana below, as the preceding 

 statements imply, and unconformable with the Eocene (Tertiary) 



