84 /. Hall on the Cretaceous Strata of the United States. 



Prom the facts before nSj it appears, that Nos, 4 and 5 of the 

 Upper Division, which are so largely deyeloped on the upper 

 Missouri, become gradually attenuated towards the south and 

 southwest, and lose in a great measure their distinctive fossils. 



The observations made in the coarse of the Boundary Survey, 

 and in all the other surveys in the southwest, show the occur- 

 rence of various colored sandstones and clays below the fossil- 

 iferous beds identified, as above, with Nos. 2 and 3 of the 

 Nebraska section. Indeed we have evidence, from numerous 

 observations, of the occurrence of a similar sandstone at so 

 many points from Missouri to New Mexico, as to render it cer- 

 tain that the formation is continuous over this wide extent of 



country. 



The observations of Mr. Marcou, on the line traversed by one 

 of the Pacific Kailroad Surveys, induced him to regard these 

 sandstones as of older date thaii the cretaceous formation. In 



(t 



(Bulletin Soc- GeoL de 



France, tome xii, p. 878,) he recognizes^ a series of sandstones 

 and clays beneath limestones Avhich are of unquestionable cre- 



taceous age. 



Corresponding to Nebraska Section 2 and 3. 



White ailiceoua limestone. 



Sandy limestone of a deep yellow color, 



Correaponding to Nebragka section 



No. 1. 



C Blue clay, 30 feet. 



White sandstone, 2j feel- 

 Hard yellow Bandstone, PO feet. 



White sandstone, 8 feet. 



2(KJ feel. 





it 



e. 



Bed of variegated marls in contact -ff^ith the Jurassic formation." 

 Alternations of calcareo-argiliaceous marls of variegated colors, 

 and -white)." 



Bed of Grynhcea dilitaia and of O&trea Marshlir* 



(Red, green 



Haviug examined tlie specimens in Mr. Marcou^s collection 

 from tliis locality, I have no hesitation in saying tliat the speci- 

 mens labelled hv him Onjphrta Tucumcarii^ {— G. dilalala, var. 



Gryphcea Pilcheri of Morton, and present no features cither in 



* These explanations nf the section quoted above are those given by Mr. Marcou. 

 The de^gnations at the right hand are uiose given by him in the text accompanying 

 the section. 



