10 ■ ^'EW YORK STATE MUSEUM 



they accumulated are not thorouglil}- understood. The formation 

 is called the Beekmantown limestone, but was known as the 

 Oakiferous fornaation till recently. It is ako thickest im the 

 northeastern Adiix^ndacks aaad diminishes in thickness to the 

 south and west, so that near the region under immediate consid- 

 eration it also disappears and the next succeeding formation is 

 found resting on the old land surface. Within the limits of the 

 map the different layers of the Beekmantown formation succes- 

 sively overlap on the old surface, so that a thickness of over 400 

 feet at Little Falls has diminished to nearly or quite zero at the 

 northern limit of the sheet. The overlap is beautifully shown 

 around Diamond hill, a low mound of the old land surface, and 

 will be later described in detail. 



Following the Beekmantown, a marine, fossiliferous limestone, 

 the Trenton formation, was deposited, with two thin lower mem- 

 bers, the Lowville (Birdseye) and Black River limestones. This 

 formation was very unequally deposited and shows a very rapid 

 diminution in thickness toward the east in the restricted dis- 

 trict under consideration. The Lowville is a pure, drab, thick 

 bedded limestone in which calcite-filled tubes abound, and is the 

 main quarry rock of the district. The Black River is a massive, 

 black, brittle limestone usually, and is only here and there pres- 

 ent in the district, the Trenton usually following the Lowville 

 directly. The Trenton is thin bedded and usually gray, though 

 with some black layers, and many of the beds are a mass of 

 fossil shells. 



Toward the close of the Trenton, fine muds began to be washed 

 into the previously clear sea, at first intermittently, producing a 

 series of alternating limestone and shale bands, later more con- 

 tinuously, giving rise to the fine muds of the Utica formation. 

 The abundant clear water life departed and was replaced by 

 a different and much sparser assemblage of forms. During the 

 deposition of this formation it seems probable, from several lines 

 of evidence, that the present Adirondack region was either wholly 

 submerged or else so nearly so that only a few small islands 

 were left protuding above the water. Here ag-ain the deposit 



