I /. Hall on the Cretaceous Strata of the United States. 85 



form, character, condition of preservationj or otlierwisej wliicli 

 can serve to distinguish them from GryplixEa Pitcher i in the 

 Boundary Survey collcctionSj from strata forming a continuation 

 of the Llano Estacado."^ 



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

 the exhibition of the sandstones and clays, beneath the limestone 

 with Qryplicea Pitcheri is extremely interesting, as giving the 

 succession of beds with lithological character, more in detail than 

 has elsewhere been published from that region.f 



The results at which I have arrived in regard to the identity 



of the western and southwestern cretaceous formations, may be 



4 more clearly appreciated by a comparison of sections of the 



Upper Missouri and of the same formations on the line of the 

 Boundar^^ Survey. 



Section of the Llano Estacado^ and the Prolongation of the same 



beds to the southward. 



4. Tertiary sandstone, conglomerates, etc., with clays and im- 

 pure limestones. (Resting unconformably upon the strata below.) 



3. Dark colored argillaceous limestone, frequently composed 

 largely of broken shells, and containing Exogyra costata.^ 



2. Yellow or buff colored limestone, arenaceous limestone, 

 clays, &c., with Inoceramus problematic us ^ Gryphcea PitcKeri^ 

 Ammonites Texanus^ Toxastcr Texanum^ Pyrina Parryi^ &c. 



1. Sandstones and clays, of a white, gray, or red color, con- 

 taining few or no fossils, in the southwest. 



I 



Section of the heds^ seen on the Missouri River^ from Dixon^s 



Bluff to Fort Pierre^ and thence to the Mauvaises Terres. 



4. Tertiary sandstones, conglomerates, argillaceous limestone, 

 clay, &c. 



3. Light colored calcareous clay, and dark colored astringent 

 clay, with nodules of limestone. (This includes Nos. 4 and 5 of 

 the original Nebraska section.) 



2. Gray or buft-colored, and blue or lead-colored argillaceous 

 limestone, clay, etc., containing Inoceramus prohlematicus^ Am- 

 moniteSj &;c. (This include Nos. 2 and 3 of the original Nebraska 

 section.) 



* TIic specimens from Pyramid Mountain are figured in the report of the survey 

 I of the 36th Parallel, chup. ix; and those of the Boundary Survey "will be found in 



the present volume. The Ostrea which usually accompanies the Gryjphc^a Pitcheri 

 is 0, subovata of Shumard. 



f For local sections in detail, of the formation No. 1, see Report of the Boundary 

 Surrey. 



f It is quite probable that these beds may not be separable in all cases, from those 

 below, and I am now informed (May 1857) by Dr. G. G. Shumard that he finds 

 Exogyra cosiata exteuding throughout the fos.siliferou8 cretaceous strata of New 

 Mexico. 



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