56 NEW YORK STATE MUSEUM 



Metamorphism and alteration. Brecciation has been noted 

 along both margins of the strip. Fracturing has been extensive, pro- 

 ducing many small cracks that have been healed by calcite. The 

 broken surfaces of the rock along the eastern margin of the strip 

 show by the smooth, distorted blackened depressions that there has 

 been some movement in the rock. The alteration is least where the 

 beds are flattest. The principal changes then are due to granulation 

 which usually has been sufficient to conceal or destroy organic 

 remains. 



Summary. Presumably the Upper Cambric beds are followed 

 in this strip by the Beekmantown (Calciferous), as is the case in 

 the central strip; but fossils belonging to this horizon have not yet 

 been discovered. This terrane may be represented by all or part of 

 the dolomitic strata shown in the Stoneco quarry and their apparent 

 equivalents to the north. ^ 



Locally about Saratoga a very fossiliferous limestone lens appears 

 in the basal portion of the dolomite formation. - 



The trilobites discovered by Professor Dwight on the Spackenkill 

 road, as mentioned on page 49, were like those discovered by Mr 

 Walcott at Saratoga.^ 



No fossils have been reported from the limestone on the western 

 bank of the Hudson within this quadrangle. In 1879 R. P. Whit- 

 field* reported Maclurea magna from these limestones at 

 Newburgh and in 1880 W. B. Dwight'^ found an assemblage of 

 Trenton fossils in that city. 



^ The description of the cherty, dolomitic limestone at the Stoneco 

 quarry and overlying the Potsdam beds along the Spackenkill road was 

 written in October 1909. At the meeting of the Geological Society at 

 Cambridge, Mass., the following December, Professors Ulrich and Cush- 

 ing described a dolomite in the Mohawk valley which " is found to con- 

 sist of two distinct formations, the lower a dolomite formation of Ozarkic 

 age, the upper a limestone of Lower Beekmantown age with a distinct 

 unconformity between the two." The Beekmantown was described as 

 thinning to the west, so that west of Little Falls the Lowville rests on 

 the Ozarkic. The unconformity may be followed into the Champlam 

 valley, reappears in the St Lawrence region " and is believed to mark 

 the line of division between the two formations everywhere in northern 

 New York." 



2 Preliminary list of papers. G. S. A., 22d winter meeting at Boston- 

 Cambridge, December 1909. 



3 See Thirty-second Ann. Rept. N. Y. State Mus. ; also U. S. G. S. Bui. 30, 

 p. 21, and Science, 1884, 3:136-37. 



^Amer. Jour. Sci., Ser. 3, 18:227. 

 ^Amer. Jour. Sci., Ser. 3, 19:50-54. . 



