138 GEOLOGY AND PALEONTOLOGY. 



trace from Nebraska to New Mexico, and which are likewise, over a large part, or the whole 

 distance, underlaid by sandstones, etc. 



With regard to the two hundred feet of sandstones and clays below a of the Pyramid moun- 

 tain, these may be a distinct formation, or they maybe a part of the same formation as the beds 

 above. Of all the collections yet examined from the southwest, not a single fossil from beds 

 below those containing Grypluea Pitcheri, and its associated fossils, has come under my notice. 

 We are, therefore, without the means of identification at the present time. 



The sandstones of the northwest have a great development, and it is not probable that we yet 

 know their full thickness or their relations throughout. The collections made by Dr. Hayden, 

 at the mouth of the Judith river,* contain a single genus, Hettangia, which, in Europe, is con- 

 sidered as restricted to the Liassic epoch. This, however, is associated with cretaceous types, 

 and though there is some evidence in favor of a reference to the Jurassic period, we have not 

 satisfactory proof. 



The results at which we have arrived in regard to the identity of the western and south- 

 western cretaceous formations, may be more clearly appreciated by a comparison of sections of 

 the upper Missouri and of the same formations on the line of the Boundary Survey. 



Section of the Llano Estacado and the prolongation of the same beds to the southwest. 



4. Tertiary sandstone, conglomerates, etc., with clays and impure limestones. 



3. Dark colored, argillaceous limestone, frequently composed largely of broken shells, and 

 containing Exogyra costata. 



2. Yellow, or buff colored limestone, arenaceous limestone, clays, etc., with Inoceramus 

 problematicus, Gryphcea Pitcheri, Ammonites Texanus, Toxaster Texanum, Pyrina Parryi, etc. 



1. Sandstones and clays of a white, gray, or red color, containing few or no fossils. 



Section of the beds seen on the Missouri river from Dixon's Bluff to Fort Pierre, and thence to 



Mauvaises Terres. 



4. Tertiary sandstones, conglomerates^ argillaceous limestone, clay, etc. 



3. Light colored calcareous clay, and dark colored astringent clay, with nodules of limestone. 



2. Gray or buif colored, and blue or lead colored argillaceous limestone, clay, etc., containing 

 Inoceramus problematicus, Ammonites, etc. 



1. Sandstones and clay, white, gray, or brown, in irregular and unequal alternating beds, 

 containing few fossils beyond fragments of carbonized wood. 



I can, therefore, only regard the sandstone of the southwest, or at least a large part of it, as 



identical in age and a prolongation of the formation No. 1 of Nebraska, and which, from the 



evidence of its cretaceous character and the absence of any evidence to the contrary, I refer to 



the cretaceous period. 



•* Tbe formation at the mouth of the Judith river, containing a group of fossils quite distinct from any heretofore 

 described, has been referred by Messrs. Meeli and Hayden, provisionally, to No. 1 of the Nebraska section, from its general 

 lithological analogy, and from position ; but at that point the beds 2 and 3 are wanting, these fossiliferous beds lying imme- 

 diately below No. 4 of the section. 



