684 



INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



This clay is important for the reason that it is unlike the general type of clay found at 

 Boston. All the Pleistocene clays of the vicinity are of blue-gray to brown or buff colors; this 

 clay is Hght gray to nearly white. The Pleistocene clays contain numerous bowlders and peb- 

 bles composed of all kinds of rock found in New England, but in this clay only two bowlders 

 have been discovered, and these consist of rock only found in the vicinity of Boston, and which 

 forms the bedrock of the region. The Pleistocene clays are interstratified with glacial deposits; 

 this clay rests on bedrock and is separated from the overlying Pleistocene clay by a bed of till. 

 This clay is much dryer than the overlying Pleistocene clay. * * * 



Samples of the white clay from the Ames Building boring were compared at the office of 

 the United States Geological Survey with samples of clay collected by Mr. Veatch from a num- 

 ber of borings on Long Island, New York, and found to agree very closely with them in appear- 

 ance. Mr. Veatch has correlated the Long Island deposits with the Raritan formation of New 

 Jersey. If this correlation is correct, it is possible that the Boston deposits may be of similar 

 age. This is rendered more probable by the similarity of the material in the Boston borings to 

 some of the clays on Marthas Vineyard. 



K-Ii 12-13. NORTHERN WYOMING. 



The Bighorn Basin, in northern Wyoming, is surrounded by Cretaceous strata 

 which Fisher ^^'^ described under the names Morrison, Cloverly, Colorado, Pierre, 

 and Laramie and associated formations. Recent surveys by Woodruff ^''^ yield the 

 following section of the southwestern portion of the Bighorn Basin : 



Section along ShosJione River near Cody, Wyo. 



System. 



Formation. 



Thickness 

 (feet). 



Characteristics. 



Tertiary. 



Cretaceous. 



Wasatch formation. 



Unconformity. 



Fort Union formation. 



Unconformity (?) 



Laramie (?) formation. 



[See p. 774.] 



3,100 



[See p. 774.] 



2,630 



Dull green sandy shale with local brown leaf -bearing beds 

 and gray massive sandstone. 



ft 



3 



Und iff erentiated 

 Montana. 



760 



In lower part gray massive sandstone and dark-colored sandy 

 shale in alternating layers; in upper part dark and light 

 gray shale alternating, and numerous hgnitic beds. 



Eagle sandstone. 



220 



Gray massive sandstone, weathering tan, and gray sandy 

 shale with dark coaly bands. Locally coal bearing. 



Colorado shale. 



3,375 



Black to dark-gray shale with rusty sandstone at base and 

 gray massive sandstone at short intervals in lower half. 

 Thin beds of coal occur a httle below the middle. 



Cloverly formation. 



300 



Gray, green, and maroon shales and gray compact sandstone. 



As shown in the above table, the thickness of sandstone and shale between the top of the 

 Colorado formation and the great unconformity at the base of the Wasatch formerly mapped 

 by Fisher " as "Laramie and associated formations" is here tentatively subdivided into Eagle, 

 undifferentiated Montana, Laramie (?), and Fort Union. These formations are suggested on 



i Fisher, C. A., Prof. Paper U. S. Geol. Survey No. 53, 1906, p. 8. 



