1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 195 



Terse jointings. These polarize only in dull colors, give extinctions 

 parallel to the axis of elongation, and are believed to be sillimauite. 

 Besides these are occasional minute elongated crystals, quite opaque, 

 and with a bright, brassy-yellow reflection, which are doubtless pyrite. 

 The above completes the list of determinable constituents. The rock 

 belongs, therefore, to the variety of peridotite called picrite by Professor 

 Eosenbusch. A partial analysis by Mr. L. H. Merrill, of the Maine 

 Experiment Station, yielded results as follows : 



Per cent. 



SiO, 38.01 



A1 2 3 5.32 



Fe 2 3 6.70 



FeO 4.92 



MgO 23.29 



CaO 4.11 



K 2 22 



Na 2 4.15 



Ignition 10.60 



Specific gravity 2.83 



The nearest observed outcrop of the shale was some hundred yards 

 distant. The rock has become indurated until it is now a very flue and 

 compact quartzite, weathering whitish, and somewhat resembling on 

 casual. inspection a weathered felsite. As an equal amount of indura- 

 tion exists in samples collected a long distance from the outcrcp, and? 

 moreover, as is well known, coutact metamorphism iu rock so basic in 

 composition is reduced to a minimum, I can not consider this induration 

 as at all dependent upon or connected with the ejection of the mass of 

 peridotite. The results of the violent chemical action so graphically 

 described by Dr. Jackson are no longer apparent, if, indeed, they ever 

 existed. 



A thin section cut from a specimen taken from a dike some 6 feet in 

 width, lying nearly in a direct line between the peridotite and Deer 

 Isle Landing, showed the rock to be a diabase of the ordinary type. 



National Museum, March 10, 1888. 



