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EDWARD STEIDTMANN 



differential metamor phism of limestones after their emergence from 

 the sea. — In a succession of conformable formations, each forma- 

 tion usually presents a certain specific lithologic unity of character 

 which is different from that of adjacent formations, and may or 

 may not be related to them by gradation phases. Thus limestones 

 are not infrequently sharply interstratiried with dolomites, and 

 give by their color contrasts a graphic portrayal of the sharp 

 lithologic difference which frequently distinguishes adjacent 

 carbonate formations. Attention is directed to a number of 

 typical illustrations of sharply defined stratigraphic cleavage 

 between limestones and dolomites. The "lead and zinc" district 

 of southwestern Wisconsin presents the following interesting 

 succession: 



A striking case of sharp interstratification of nearly pure lime- 

 stone beds and dolomites is described by F. B. Peck 1 as occurring 

 in the Trenton of Lehigh and Northhampton counties, Pa. 



LP. Lesley's 2 study of the Cambro-Silurian limestones of Cum- 

 berland County, Pennsylvania, is perhaps the most detailed 

 quantitative chemical study of a limestone section which has ever 

 been made from the viewpoint of throwing light on the origin of 

 limestone and dolomite. The section studied was about 375 feet 



1 F. B. Peck, Eco. Geol., III, No. 1, p. 43- 



2 1. P. Lesley, Second Geol. Survey Fa., Vol. MM (1897), pp. 311-62. 



