QUARRY MATERIALS OF NEW YORK IO5 



interspaces and is also granulated. The biotite occurs in small 

 scales, which here and there have been converted into chlorite. 

 Iron ores occur very sparingly. The granite may be considered as 

 a fair material for crushed stone or paving blocks and well adapted 

 for all foundation work. 



GRANITE AT HORICON, WARREN COUNTY 



An occurrence of granite at Horicon, on the outlet of Brant lake, 

 Warren county, has supplied some building stone in an experi- 

 mental way. It has not attracted much attention for commercial 

 quarry purposes, owing to its remoteness from the railroad and 

 difificulties of getting the material into the market. The present 

 interest is mainly connected with the rather unusual nature of the 

 rock which differs from that of normal granites. 



The rock has a porphyritic appearance owing to the presence of 

 pink feldspars, which measure up to an inch long and are rather 

 thickly distributed through a groundmass of dark gray color which 

 is composed of greenish feldspar, quartz and biotite. The large 

 feldspars give an attractive pattern and a warm tone to the polished 

 surface. They belong to the microcline variety and are developed 

 in stout prisms that are usually twinned and occasionally granulated 

 and squeezed into lenticular form. The greenish feldspar of the 

 groundmass is a plagioclase identified as oligoclase. It forms 

 rounded grains 2 or 3 mm in diameter. The biotite occurs in even 

 smaller particles, but so abundantly as to lend a dark color to the 

 body of the rock which, apart from the feldspathic constituents, 

 has the character of a biotite schist. 



The rock in fact is really a modified schist, the original of which, 

 consisting of biotite and cjuartz with subordinate feldspar, has been 

 drenched with solutions or vapors from a neighboring granite mass. 

 The presence of the latter at least as an underlying body, is indi- 

 cated by numerous pegmatite dikes, some of large size, that are 

 exposed in the vicinity and that contain the same feldspar in- 

 gredients as the schist itself. In the vicinity of the dikes the 

 granitic material increases in proportion to that of the original 

 schist and the rock becomes lighter colored and coarser in grain. 

 The groundmass is more or less recrystallized and largely absorbed. 

 The impregnation of hornblende and biotite schists by granites is a 

 common feature of Adirondack geology, but usually it leads to the 

 formation of striped or leaf gneisses in which the original schist 

 and the granite alternate in parallel bands. In the present instance, 

 however, the added igneous material lacks any definite arrange- 



