GEOLOGY OF THE BROADALBIN QUADRANGLE 29 



Downward the Theresa formation is in no sense sharply sepa- 

 rated from the Potsdam and no distinct line can be drawn. Even 

 in what must certainly be regarded as Potsdam, an occasional thin 

 layer of limestone occurs. Upward the transition to the Little Falls 

 dolomite is less gradual, the top of the Theresa, within the quad- 

 rangle, apparently being marked by a rather massive bed of sand- 

 stone of unusual thickness (five feet) and prominence. This sand- 

 stone bed, which has heretofore been mistaken for the Potsdam, 

 outcrops one-half of a mile south of Mosherville ; one-fourth of a 

 mile southwest of Parks Mill ; one and one-third and two miles west 

 and one and one-half miles southwest of Galway ; one-half of a mile 

 north-northeast of West Galway; in the northern end of Gifford 

 valley, etc. What appear to be small cryptozoon forms, not over 

 an inch in diameter, have been noted one-fourth of a mile east of 

 North Galway; one mile northwest and one and one-half miles 

 southwest of Galway. Oolite has been observed one-fourth of a 

 mile east of North Galway and also in drift fragments three-fourths 

 of a mile east of Northampton. 



Within the map limits no fossils (except cryptozoon) have been 

 found and the relation of these beds to the fossiliferous Hoyt lime- 

 stone of the Saratoga region is not exactly known. While it is 

 possible that the upper part of the Broadalbin passage beds may 

 correspond to the Hoyt limestone of Saratoga, it is certain that the 

 Hoyt limestone, as such, does not reach the Broadalbin sheet nor 

 do any of its fossils so far as known. In view of these facts the 

 writer finds it necessary to class together all the transition beds as 

 Theresa and so map them on the Broadalbin sheet. 



No continuous section has been found within the map limits but 

 a mile south of East Galway, there is an excellent section showing 

 all but the uppermost beds in nearly continuous outcrop down to 

 the Potsdam. The thickness is here approximately two hundred 

 feet with perfect transition to the Potsdam well shown. Westward 

 from this locality to Parks Mill and Mosherville there are many 

 outcrops of the Theresa formation. Another excellent display of 

 the formation is in the ridge between Galway and the Amsterdam 

 reservoir where the lowest beds are not visible but the thickness 

 must be nearly two hundred feet. 



According to LHrich and Gushing^ the Hoyt limestone, close to 

 one hundred feet thick near Saratoga, is regarded as a basal phase 

 of the Little Falls dolomite and the Theresa (passage) beds are 



1 N, y. State Mus. Bui. 140, p. 99, 112. ' 



