GEOLOGY OF THE VICINITY OP LITTLE FALLS 27 



There is however no copper at all in the rock and the green spots 

 appear to be constituted of glauconite.^ 



A certain amount of mineralization is sometimes to be noted in 

 some of the layers of the formation, zinc blende (sphalerite), 

 galena, pyrite and chalcopyrite all occurring, though always in. 

 small quantity. 



The Beekmantown formation is overlain by a pure gray lime- 

 stone known as the Lowville. The Chazy limestone lies at this 

 horizon along Lake Champlain, but does not appear in the Mohawk 

 valley. Its absence is due to a cessation of depiosition in the 

 Mohawk region and an uplift which probably raised the district 

 slightly above sea level, sufficiently to stop deposition, but not 

 sufficiently to permit of much wear. This uplift likely involved 

 all of the State except the Champlain region, and persisted 

 through the latter part of Beekmantown time and throughout the 

 Chazy. Then subsidence was renewed, though but slowly at first.^ 



In the Little Falls district the upper boundary of the Beekman- 

 town is not everywhere sharp, a grading into the Lowville through 

 a series of passage beds of intermediate character being often 

 seen, as was first noted by Prosser.^ These beds are of no great 

 thickness, 8 feet being the maximum noted by the writer, along 

 White creek nearly 3 miles north of Middleville. Prosser meas- 

 ured 11 feet at Newport on West Canada creek not far west of the 

 map limits. These beds are of too slight thickness and too inter- 

 rupted to map separately on a map of this scale, and have been 

 therefoT-e included with the Beekmantown, the base of the Lowville 

 being made at the first pure limestone stratum. 



^Glauconite is a mineral of varying composition, but essentially a silicate 

 of iron and potash. In sedimentary formations it lias often a close 

 association with the skeletons of minute organisms ; and, since the chert 

 is likely of organic origin, the association is a natural one. It is not at 

 all indicative of any mineral content of value in the bed. 



^The Chazy formation is over 800 feet thick toward the lower end of 

 Lake Champlain, and diminishes rapidly in thickness to the south and 

 west till it wholly pinches out. Moreover the entire Lower Paleozoic 

 rock' series is thickest on the northeast, diminishing thence west ahd south, 

 so that more profound subsidence appears to have characterized the former 

 region throughout. 



= N. Y. State Geol. 15th An. Rept. 1895. p.627-31. 



