FORMATIONS AM) PHYSICAL HISTORY 



539 



it has Urn affected by intrusions of igneous rock. The areas of 

 Laramu- o>;il an- indicated in Fig. 438. 



Transition beds between Mesozoic and Cenozoic. 1 There are 

 divrrs, more or less local, terrestrial formations in the west which 

 ha vi- Urn referred now to the Cretaceous (Laramie, or more 

 exactly, to the upper Laramie or post-Laramie), now to the Tertiary 



Fig. 454. An outcropping ledge of clay, hardened by the burning of the coal- 

 bed below. Except in the immediate vicinity of the burnt-out coal-bed, the clay 

 is not indurated. Near Buffalo, Wyo. (Black welder.) 



(Eocene). These formations are, generally speaking, unconform- 

 able on the Laramie, and in some places seem hardly separable from 

 the recognized Tertiary 2 (Fort Union). Their reference to the 

 Eocene seems to be justified both on stratigraphic and paleontologic 

 grounds, so far as present data are concerned. 



Pacific coast. The Cretaceous system is represented on the 



1 The questions involved in the formations here referred to are discussed in 

 the following recent papers: Stanton, Am. Jour. Sci., Vol. XXX, and Wash. Acad. 

 Sci. Vol. XI; Knowlton, Wash. Acad. Sci., Vol. XI, and Am. Jour. Sci., Vol. XXXV; 

 Stone and Calvert, Econcm. Geol., Vol. V; Lee Am. Jour. Sci., Vol. XXXV; and 

 Cross, Wash. Acad. Sci., Vol. XL 



2 Here belong the Arapahoe, Denver, Raton, Monument Creek and perhaps 

 other beds of Colorado, the Carbon, Evanston, and Lance (Ceratops) beds of 

 Wyoming, and the Lance formation, and part of the Livingston beds of Montana. 



