LOCATION, CHARACTER, AND FAUNA OF TILE SECTIONS 267 



cheanus Cragin, both of which are Washita species. Between this marine 

 shale and the Morrison are the rocks which Darton mapped as C loverly, 

 including a conglomerate identical in character with the conglomerate 

 above the Morrison in the Lander section. Again the question must be 

 raised, What is Dakota in this section? Is it the sandstone next below 

 the Mowry? Is it this sandstone plus the underlying shale, plus, per- 

 haps, a part of the lower sandstones? Or is it entirely represented in 

 the rocks which Darton here called Cloverly? The fossils do not give a 

 decisive answer. They are of types represented by similar forms both in 

 the Comanche and in later Cretaceous formations. The same interpreta- 

 tion that was suggested for the Lander section seems reasonable here. 



All along the foothills of northern Colorado the Cretaceous section 

 differs from the eastern Wyoming section only in minor details. I have 

 selected as typical the section west of Fort Collins (number 10 of the 

 chart). The Greenhorn limestone is better developed, becoming consid- 

 erably thicker southward, while the Mowry shale ceases to be recognizable 

 as a distinct unit. In other respects, save for varying thicknesses, the 

 sections of the ?ocks closely associated with the Dakota are practically 

 identical. The marine shale between the sandstones which have here been 

 referred to the Dakota is well developed and contains, in addition to the 

 fossils collected at Horse Creek, one or two other species of Inoceramus, 

 some simple forms of Ostrea, and an Anchura. This fossiliferous shale 

 with the same small group of species was examined by me in 1906 at 

 many points between Fort Collins and Boulder. Some of the localities 

 near Boulder were visited in company with Prof. Junius Henderson, who 

 has since briefly discussed 15 the horizon and extended its known distribu- 

 tion to the northern boundary of the State. Its faunule has just been 

 described, illustrated, and discussed in a paper by J. B. Reeside, Jr., ac- 

 cepted for publication in the "Shorter contributions to general geology v 

 of the United States Geological Survey. 16 



In 1905 I had the privilege of joining W. T. Lee in a field review of 

 a number of localities in southeastern Colorado, northwestern Okla- 

 homa, and northeastern New Mexico where a characteristic Comanche 

 (Washita) fauna 17 is found in beds between two sandstones, both of 

 which have been called Dakota and the upper one doubtless is Dakota. 

 We found Gryphcea corrugata and associated Washita forms at Two 



15 Junius Henderson : The foothills formations of north central Colorado. Colorado 

 Geol. Survey, 1st Kept., 1908, pp. 172-178 ; Colorado Geol. Survey, Bull. 10, 1020, pp. 

 83-85. 



16 tl. S. Geol. Survey, Professional Paper no. 131. 



17 T. W. Stanton: Morrison formation and its relation with the Dakota formation. 

 Jour, of Geology, vol. 13, 1905, pp. 657-669. 



