62 J. F. Kemp — Minerals near Port Henry, JV. Y. 



length for which an objective is corrected should always be 

 stamped on its mounting along with the record of exact focal 

 length and numerical aperture. 



If there be accurate labeling of optical tube-length, and of 

 the equivalent focal length of eye piece and objective, the 

 camera lucida ceases to be a necessity to the user 01 the micro- 

 scope. Under present conditions, however, and until better 

 methods are adopted by the majority of manufacturers, it is 

 the only read} 7 means of approximating toward the correct 

 measurement of microscope magnification. 

 Brooklyn, K Y., April 2, 1890. 



Art. Y. — Notes on the Minerals occurring near Port 

 Henry, N. Y. ; by J. F. Kemp.' 



During the summer of 1889 the following notes on minerals 

 occurring near Port Henry, N. Y., were made, largely with 

 the aid of Mr. W. H. Benedict, then in charge of the local 

 high school. At the abandoned Pease quarry, a short distance 

 northwest of the town, a face of white crystalline limestone 

 has been laid bare, and in this occur streaks consisting chiefly 

 of hornblende, plagioclase, muscovite and quartz, but contain- 

 ing as well a great abundance of yellowish brown titanite crys- 

 tals. These latter average perhaps an inch, along c, bj one- 

 half inch along o\ and are bounded by large 2P and OP and 

 less prominent 00P06 and ooP — making the common semeline 

 type. Individuals appear to have been wrenched or broken, 

 possibly by mountain-making action. Fine brown tourmalines 

 occur with them in the same associations and are also wrenched 

 and bent. In one instance a crystal one and one-half inches 

 long, is bent around through at least 70°, yet without notable 



fracturing. West of the 

 Pease quarry is a quarry 

 where flux was being obtained 

 for the local furnaces. The 

 rock is a beautifully clear 

 crystalline limestone with ex- 

 cellent, small, hexagonal tables 

 of graphite disseminated 

 through i t . Occasionally 

 lemon yellow calcite is found, 

 but of especial interest are the 

 fine crystals of clear calcite of 

 the general outline of the unit R with a low striated four-faced 

 pyramid imposed on each R face, and often truncated by R 



