32 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull. ICO. 



species of fossils have been found at several places well up in the series. 

 I have collected Inoceramus cripsii, Mactra alia, Cardium, Baculites 

 compressus, sm&Placenticer as placenta, var. inter calaris, in Man cos canyon 

 from a bed that seemed to be 800 to 1,000 feet above the base of the 

 coal bearing sandstones. No evidence of faulting was seen there. It 

 is beyond the scope of this paper, however, to discuss either the age of 

 these upper beds or the more general subject of the delimitation of the 

 Laramie formation. There is need of much detailed work in some parts 

 of the supposed Laramie area, and the evidence from all possible sources 

 must be collected and considered before the latter question can be dis- 

 missed with a final solution. 

 The shales of the middle division attain a thickness of 1,200 to 1,500 



feet in the San Juan valley, and farther north in western Colorado they 

 are still thicker. It has already been intimated that these shales are 

 of much the same character throughout and are apparently the product 

 of continuous sedimentation, but the characteristic fossils of the Colo- 

 rado formation are confined to their lower half. The upper half is 

 usually barren of fossils, though a few species belonging to the Mon- 

 tana fauna have been found at the top. Along the Mancos river north 

 of Mesa Verde and in the valley of Animas river where I have made 

 collections the fossilifcrous zones are as follows: * 



Feet. 



1. Soft dark clay shales resting on Dakota sandstone. Numerous specimens of 



Gryphaea newberryi in upper portion 120 



2. Light drab argillaceous limestone with Inoceramus labiatus. This is seldom 



exposed and probably not continuous 4-6 



3. Dark clay shales with a large Inoceramus covered with Ostrca congesta, and 



calcareous concretions, a few of which contain Inoceramus and Baculites 

 gracilis f 250 



4. Thin bands of brown arenaceous limestone and occasional concretions alter- 



nating with shales. Fossils abundant, including Inoceramus labiatus, I. 

 frayilis, I. dimidius, Ostrca lugubris, and Prionocyclus macombi 8-10 



For about 200 feet above this zone there are fragments of a large 

 Inoceramus, apparently like 1. deform is, covered with Ostrea congesta. 

 No fossils were found in the 600 or 700 feet of shales above this horizon. 



Although the fauna of these beds is not large it contains several 

 characteristic species and it is believed to prove that the fossiliferous 

 beds above described are the approximate equivalent of the Colorado 

 formation and that the overlying shales should not be included in that 

 formation. Wherever fossils have been reported from the upper half 

 of the shale division in western Colorado and eastern Utah they are 

 of Montana formation species and the two faunas never seem to be 

 blended 1 in that region. 



Northward, in the valleys of Grand and Gunnison rivers and their 

 tributaries in Colorado and of Green and Price rivers in Utah, the 



1 Mr. W. H. Holmes reports the occurrence of Graphites warreni, Inoceramus barabini,nnd Baculites 

 ovatus in the same lied on the San .! nan river from about the horizon of the zone No. 4 above described. 

 I have been unable to find this collection, but 1 have reason to believe that the last two species were 

 incorrectly identified. 



