VOL XI 



PROCEEDINGS OF THE NATIONAL MUSEUM. 597 



darker color, and so far as observed never showed under the microscope 

 traces of residual pyroxene. Wherever, too, this darker variety of ser- 

 pentine occurred in patches of any considerable size it was observed 

 that it frequently contained iuclosures of graphite scales. For the 

 study of this variety of the rocks, material was selected from the quarry 

 of Mr. J. E. Reed, some miles west of Port Henry. From this open- 

 ing was selected four series of specimens, characteristic of the rocks 

 as there occurring. These were(l) themerchautableophiolite, a granular 

 rock consisting apparently of about equal proportions of snow-white 

 calcite and dark green serpentine (70082); (2) a similar textured rock, 

 but of more uniform green color, the serpentine and calcite being less 

 distinctly differentiated, and the calcite being moreover of aclearglassy 

 appearance, and for this reason less notable; (3) masses from an inch 

 to a foot or more in diameter, consisting mainly of deep though dull 

 greeu serpentine, and often carrying large scales of graphite (70083); 

 and (4) samples of the same shape and mode of occurrence, but con- 

 sisting of a central portion or nucleus of coarse massive calcites and 

 graphite scales, surrounded by a ring or zone of varying thickness 

 of the dull green serpentine (700S4). The last three forms occur spo- 

 radically throughout the beds, and as their presence is objectionable in 

 the quarried blocks they are often the cause of considerable waste. 



Sections from the two first-mentioned varieties showed the rock to 

 consist essentially of calcite, serpentine, and dolomite. Rough deter- 

 minations of the relative proportions of the various constituents 

 were made by dissolving out from weighed portions of the pulverized 

 rocks the calcite by acetic acid, the dolomite by cold hydrochloric 

 acid, and in each case weighing the residues. Calculations from these 

 results showed No. 1, the typical ophiolite, to consist of 52 percent, 

 calcite, 15 per cent, dolomite, and 33 per cent, serpentine; the second 

 variety yielded, under like treatment, calcite 72 per cent., dolomite 2 

 per cent., and serpentine 26 per cent. An analysis of the dark serpen- 

 tine out of the typical ophiolite (70082) from this quarry by Mr. Cat- 

 lett yielded results as follows : 



Si0 2 39.9(5 



A1 2 3 1.07 



Fe 2 3 3.53 



FeO 3.85 



MgO 37.61 



NiO none. 



Cr. 2 3 none. 



MnO trace. 



H 2 13.65 



99.67 



This material it should be noted was separated out by specific grav- 

 ity and subsequent treatment with acetic acid. Under the microscope 

 the powder was of a dirty dull green color, opaque, and showed when 

 the stage was revolved between crossed uicols a somewhat fibrous or 



