GEOLOGY OF THE NORTHERN ADIRONDACK REGION 369 



Valcour. The lower part of division B is magnificently shown 

 on Bluff point, in the southern part of Plattsburg township, and 

 the full thickness, except for occasional small gaps, is well exposed 

 in the Chazy wedge between the Beekmantown and Plattsburg 

 faults in the northern portion of the town. 1 Both contacts show 

 here, and large quarries are opened in the rock. The upper divis- 

 ion is splendidly shown on Valcour island, with exhibition of both 

 contacts. It is perhaps equally well shown in Chazy township, 

 aind the middle division is also well displayed there with full 

 thickness; but, since the name is used for the full formation, it 

 can not be applied to a substage. 



Lowville (Birdseye) limestone. In the Mohawk valley the Beek- 

 mantown rocks are in many places capped by the thin limestone 

 formation to which the above name has been given. The rock 

 is mostly a gray to drab, brittle, quite pure limestone, usually in 

 rather large massive layers from 1 to 4 feet thick, though much 

 of it is thinner bedded also. It is everywhere penetrated with 

 the vertical, branching tubes of the fucoids which are so character- 

 istic of the formation, which are usually filled with crystalline 

 calcite, and whose cross sections on many surfaces give rise to 

 the bird's-eye appearance which gave the original name to the 

 formation. 



Its distribution is erratic and is a matter of considerable im- 

 portance. It is limited to the south and west sides of the Adiron- 

 dacks, in the former situation resting on the Beekmantown, and in 

 the latter apparently on the Precambric, though no actual con- 

 tact is exposed in the whole region, so far as the writer is aware. 

 The drift is very heavy in that region, and little or no work has 

 been done on the rocks since the reports of Emmons and Vanuxem 

 Avere published. Apparently the formation extends through 

 Herkimer, Oneida, Lewis and Jefferson counties and in consider- 

 able strength, but with its base nowhere showing. Toward the 

 north, in Jefferson, the Beekmantown and Potsdam formations 

 begin to appear thinly underneath. Emmons reports a thickness 

 of 30 feet near Watertown, which is probably simply an estimate. 

 This whole western contact line is in need of careful study. 



a 15th An. Rep't State Geol., p.556. 



