HISTORICAL REVIEW .VXD PIMMARY OF SECTION 165 



In his study of the jjre-Cambrian rocks of the district in 1899, Smyth 

 encountered the Theresa formation, and mapped it with and included it 

 in the Potsdam formation, as Sarle had done, though not aware of Sarle's 

 work and results.' Thus he also realized the close relationship between 

 tlie two formations and the impossibility of drawing any sharp line be- 

 tween them. 



Grabau (1906) writes of the stratigraphy of the general area, though 

 not of the immediate district.* In his paper Professor Grabau is using 

 the district as illustrative of a general proposition which he is seeking to 

 establish. He states that at Lowville, 25 miles southeast from Water- 

 town, "the Lowville limestone overlaps the preceding formations and 

 rests, with a basal sandstone, upon the crystallines." He argues that the 

 sandstone and Calciferous sandrock thinly present in the section represent 

 an arenaceous base of the Lowville and have nothing to do with the Pots- 

 dam and Beekmantown formations. In this he is unquestionably cor- 

 rect, though as a matter of fact what is actually present in tlie Lowville 

 section is probably the full thickness of the Lowville limestone and the 

 thinned shore edge of the Pamelia underneath. The section here will 

 receive further consideration later. 



SUMMARY OF TEE GENERAL SECTION 



It appears, then, that in the district north of Watertown we have four 

 separate lithologic units beneath the Black Biver limestone which require 

 areal mapping, and that these four units are separable into two pairs of 

 closely related formations with an intervening large unconformity, the 

 Potsdam and Theresa formations beneath and the Pamelia and Lowville 

 above. Eastward from the district the Potsdam sandstone may be fol- 

 lowed as a continuous formation every step of the way to lake Champlain, 

 with steady increase in thickness eastward, so that it attains a thickness 

 of 1.000 feet or more in the Champlain region. Everywhere along the 

 same line, except for a small gap in the immediate region where it is 

 absent, owing to recent erosion, the overlying Theresa formation is also 

 found, becoming to the eastward the so-called "passage beds" between 

 the Potsdam and the overlying Beekmantown.'' The Beekmantown of 



this northern area is sorely in need of detailed study. It certainly 

 thickens eastward, but precise data for making comparison between the 

 eastern and western sections are tmfortunately lacking. 



■ C. H. Smyth. Jr. : 19tli Geological State Report, p. 198. 



* Bull. Geol. Soc. Am., vol. IT. pp. o84-58.5. Science, vol. 22, pp. 531-532. 



" C. D. Walcott : Bulletin no. SI. U. S. Geological Survey, pp. 344-346. 



