GRANITIC ROCK8 



379 



of labradorite feldspar, hypersthene and biotite. Small grains of 

 pyrite and hematite are occasionally seen in the mass. The stone 

 is hard and expensive to dress but it is susceptible of a high 

 polish and is especially adapted for decorative work and for 

 monuments. The dark, polished surface, with its chatoyant play 

 of colors, contrasts well with the gray dressed surfaces. The glaci- 

 ated ledges near the quarries show little alteration due to 

 weathering, and are evidence of the durability of the stone. In 

 some of the weathered surfaces the feldspars appeared changed 

 to kaolin, and the hypersthene is badly decomposed.* 



Grindstone Island, Jefferson County. — A red granite is quarried 

 extensively on this island in the St. Lawrence river, northwest of 

 Clayton. There are many outcrops, especially on the western 

 side of the island, and small quarries have been opened at more 

 than twenty different points. 



There are three large quarries which are worked extensively 

 and with little interruption. The granite of these quarries is 

 rather coarse crystalline, red to bright red in color and consists 

 of flesh colored feldspar, quartz and mica, with very little 

 magnetite as an accessory constituent. Its resemblance to the 

 Scotch granite has given it the name of 11 International Scotch 

 granite." Examined under the microscope the feldspars show 

 kaolinization. The durability of the stone is witnessed in the 

 unaltered or scarcely altered rock which crops out on the two 

 sides of the quarry. Blocks of large size can be obtained up to 

 the limit in handling and shipping. An examination of a repre- 

 sentative specimen of this granite shows that it has a specific 

 gravity of 2.713, equivalent to a weight of 169 pounds per cubic 

 foot. The absorption test indicated 1.55 per cent, of water 

 absorbed. The loss in a dilute solution of sulphuric acid 

 was 0.13 per cent. Freezing and thawing produced no 



* Tests of the strength of this stone made by Dr. Thos. Egleston, of Columbia College School 

 of Mines, show that it stands 27,000 pounds and breaks at 29,000 pounds to the square inch. 

 Dr Egleston's series of tests made for the company show further, that when heated to a bright 

 red heat by a blast of a Bunsen burner the stone was not cracked badly; and at a temperature 

 of 800°-1350° F. and then quenched in cold water the specimens changed in color but otherwise 

 were hardly altered, except at the highest heat. "The outside of the piece was rendered 

 rather crumbly and granular * * * but the piece as a whole was still hard and resists 

 moderate blows of the hammer." [From report made to the Ausable Granite Works.] 



