24 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull. JOG. 



In Montana the Fort Benton division of the Colorado formation is 

 well represented, and the types of many of its characteristic species 

 were collected in that state. According' to Meek and Hayden 1 this 

 division attains a thickness of about 800 feet in the neighborhood of 

 Fort Benton. The following species of invertebrates have been ob- 

 tained within a few miles of that locality, but their exact vertical range 

 in the local section has not been published: 



Inoceramus fragilis. 

 Inoceramus umbonatus. 



Inoceramus exogyroides. 

 Iuoceramns teanirostratus. 

 Inoceramus undabundus. 



Pholadoraya papyracea. 



Scaphites vermiformis. 

 Scaphites ventricosus. 

 Scaphites mullananus. 

 Nautilus elegans. 



Nearly all of these have been found in the Colorado formation or its 

 equivalents at other localities and none of them is known to occur at a 

 higher horizon. 



The geologists who have recently studied the Cretaceous coal fields 

 of Montana have been unable to divide the marine portion of the Upper 

 Cretaceous into distinct formations, and the collections of fossils have 

 not been sufficient to indicate the paleontologic break if there is one. 

 The following section, adapted from Mr. W. H. Weed's paper 2 on a The 

 Cinnabar and Bozeman Coal Fields of Montana," shows the character 

 of the strata up to and including the lower portion of the Laramie. 



Cretaceous section of Cinnabar mountain, Montana. 



Laramie: Feet. 



Sandstones, containing coal 800 



Coal seam 5 



Sandstones, white, massive, cross-bedded 125 



935 



Colorado and Montana: 



Fissile, argillaceous sandstones and shales 240 



Shales, generally crumbly, with layers of black bituminous shale, and 



harder sandy ledges 450 



Shaly sandstones and limestones 225 



Sandstone '. . 40 



Sandy, splintering, gray shales and limestones 165 



Black bituminous shales 500 



Li mestone 40 



Black shales, sometimes arenaceous 400 



Sandstone 10 



Black and dark-bine shales 250 



Sandstone 15 



Sandy shales 75 



Sandstone 10 



1 Proc. Acad. Nat. Sci., Phila., 1861, p. 421 ; U. S. Geol. Sur. Terr., vol. IX, p. xxix. 

 *Bull. Geol. Soc. Am., vol.il, 1891, p. U52. 



