SIXTH REPORT OF THE DIRECTOR IOXX) II 



the Saratoga quadrangle carried on by Drs dishing and Ruede- 

 mann will be continued and concluded by being brought into con- 

 nection with the survey of the Broadalbin quadrangle by W. J. 

 Miller. 



Referring specially to the field determinations made in this work, 

 certain stratigraphic details have been perfected. 



The limestone of the Mohawk valley, which has heretofore 

 been classed as " Beekmantown," proves to be composed of two 

 unconformable members, the upper, comprising the so called " fu- 

 coidal beds," a limestone of lower Beekmantown age, and the name 

 Tribes Hill limestone has been proposed for it ; the lower is of dolo- 

 mite, is older than the Beekmantown, and the name Little Falls 

 dolomite is restricted to this member. The upper formation thins 

 westward and disappears just west of Little Falls. 



In the eastern part of the Mohawk valley the Potsdam sand- 

 stone appears beneath the Little Falls dolomite, grading up into 

 it through a series of passage beds, the two plainly belonging to 

 the same formation. At Saratoga the basal portion of the Little 

 Falls dolomite becomes locally a fossiliferous limestone, which has 

 been provisionally termed the Hoyt limestone. Over it the Little 

 Falls dolomite, but the true Beekmantown seems to be absent, the 

 Trenton limestone resting on the Little Falls dolomite. Traced 

 through Whitehall to Ticonderoga the latter is found to be directly 

 equivalent to Division A of the Beekmantown division which lies 

 unconformably beneath the remainder of the Beekmantown and 

 does not belong with it but with the Potsdam and passage beds 

 between. 



On the Broadalbin quadrangle in Fulton and Saratoga coun- 

 ties, the area comprises rocks of Precambric, Paleozoic and 

 Pleistocene ages. 



The Precambric rocks cover about one third of the quad- 

 rangle and are chiefly represented by the Grenville schists with 

 which are associated younger foliated syenite and porphyritic 

 granite as well as nonfoliated dikes of gabbro or diabase. The 

 remainder of the area is occupied by Paleozoic formations in- 

 eluding the Potsdam, Little Falls, Trenton, Utica and Lorraine 

 formations. 



Of the Precambric rocks the Grenville, in several distinct 

 areas, is by far the most common, one area alone occupying more 

 than 40 square miles. Belts of very pure quartzite are at times 

 found in the Grenville. The syenite and granite are highly 



