SIXTH REPORT OF THE DIRECTOR I909 97 



AGE AND RELATIONS OF THE LITTLE FALLS DOLO- 

 MITE (CALCIFEROUS) OF THE MOHAWK VALLEY 



BY E. 0. ULRICH 1 AND H. P. GUSHING 



Introduction 



In a recent paper Cushing made the following - statement about 

 the Little Falls dolomite : 2 



In the correlation table on a previous page the Little Falls dolo- 

 mite (the local name of the supposed Beekmantown of the Mo- 

 hawk valley) is given as the equivalent of division A of the Cham- 

 plain valley and of the Theresa formation of the Watertown region. 

 It should be frankly stated at the outset that this is the element 

 in the table whose precise position and relationship is quite uncer- 

 tain. . . Ulrich's discovery of the unconformity between divi- 

 sions A and B in the Champlain valley, necessitating the separation 

 of division A from the Beekmantown formation, at once raised 

 the question as to whether the entire Little Falls dolomite may not 

 lie below the horizon of the unconformity and hence not be Beek- 

 mantown at all, but be properly correlated with division A and the 

 Theresa formation and possibly even with the Potsdam. . . There 

 is a second doubtful matter connected with the Little Falls dolomite* 

 namely, whether or not it is a single formation. Vanuxem carefully 

 distinguished the upper portion of the formation, the so called 

 " fucoidal layers," from the remainder, and he has been followed in 

 this by most other observers in the district. . . either the bulk 

 of the Little Falls dolomite is of substantially the same age or else 

 there is an undiscovered unconformity between it and the fucoidal 

 layers. 



During the summer of 1909 an effort was made to gain the 

 information whose lack was indicated by the quotation above. 

 Cushing and Ruedemann made a careful, detailed study of the 

 section about Saratoga, following which Ulrich was shown over 

 the section. Thereafter Ulrich and Cushing studied a series of 

 sections, commencing at Ticonderoga in the Champlain valley, 

 passing south to the Mohawk and thence west to Little Falls and 

 Newport. In much of this work Ruedemann also participated. 



In the following account of the results of the work, the bulk 

 of the paper has been written by Cushing, with an occasional 

 comment or insertion by Ulrich. The section on the " Strati- 

 graphic position of the Potsdam, Little Falls and Tribes Hill 



1 Mr Ulrich's contribution to this paper is published with the con- 

 sent of the Director of the United States Geological Survey. 

 2 Geol. Soc. Am. Bui. 19:174. 



