136 GEOLOGY AND PALiEONTOLOGY. 



Having examined the specimens in Mr. Marcou's collection from this locality, I have no 

 hesitation in saying that the specimens labelled by him as Grypluea Tucumcarii {0. dilatata, 

 var. Tucumcarii, Bui. Soc. Geol. de France, tome 12, pi. 21) are the Gryphcea Pitcheri of Mor- 

 ton, and present no features, either in form, characters, condition of preservation, or otherwise, 

 which can serve to distinguish them from Gryphcea Piiclieri, in the boundary survey collections, 

 from strata forming a continuation of the Llanft Estacado.* 



In the section of Pyramid Mountain given by Mr. Marcou, the exhibition of the sandstones 

 and clays beneath the limestone, with Gryphcea Pitcheri, is extremely interesting, as giving the 

 succession of beds, with lithological character, more in detail than has elsewhere been published 

 from that region. 



For the purpose of comparison, I subjoin some detailed sections made by Mr. Meek, in 1853, 

 upon the upper Missouri, and which are collectively merged in the sandstone No. 1 of our 

 section of the cretaceous formations, as already given. 



Section at the mouth of Big Sioux river. 



Partially indurated, silicious clay, or marl, of a slightly yellow color, and showing scarcely 

 any lines of stratification. Slope of 60 feet of modern or bluff formation. 



Part of No. 1, section of Nebraska cretaceous formation . 



1. Soft, yellow sandstone, with vertical veins and joints filled with silicious oxide of iron ; 

 also, hard, horizontal seams, containing much iron, with casts of Pectunculus Siouxensis : 10 

 feet. 



2. Large, concretionary masses, 8 to 10 feet long, and 6 feet thick, consisting of hard, fine- 

 grained sandstone^ with perhaps some calcareous naatter, laminated on the weathered surfaces : 

 6 feet. 



3. Soft sandstone, like that above, with horizontally arranged concretions of siliceous oxide 

 of iron, which are often hollow. 



The three lower divisions of sandstone constitute the upper part of No. 1 of the Nebraska 

 section. They were not seen in actual contact with beds of No. 2 ; but, from their position and 

 dip relative to the other beds, there can be no doubt of the relations of the two. Subsequently, 

 Dr. Hayden has seen the beds of Nos. 1 and 2 in actual contact on the Big Sioux river. 



At a point twenty-five miles below Sergeant's Bluff there is an exposure of about 100 feet, 

 consisting of beds of sandstone and clay, which present great irregularity in bedding, some of 

 the strata rapidly expanding in one direction, while others thin out in the opposite direction. 



Section on the right-hand side of the Missov,ri river, tiuenty-five miles heloiv Sei-geant's Bluff. — 

 Successive beds, or strata, forming part of No. 1, Nebraska section of cretaceous formation. 



1. A bed of dark-gray clay, alternating above and below with soft sandstone seams. The 

 middle mostly clay ; 6 feet. 



2. Light, yellow clay, passing downwards into a very soft, gray sandstone ; 5 feet. 



3. Very dark clay, with fragments of carbonized wood ; 1^ feet. 



• The Bpecimens from Pyramid Mountain are figured in the Report of the survey of the 35th parallel, and those of the 

 boundary survey will be found in the present volume. 



