118 W. O. Crosby—Pinite in Hastern Massachusetts. 
The pinite is also found in other fragmental formations of 
this region. Underlying the Primordial beds of the Boston 
and River Parker basins, and having its best development in 
the towns of Marblehead, Saugus, Melrose, Malden, Medford, 
Dedham, and Hyde Park, is an extensive a somewhat pecu- 
liar conglomerate rock known locally as the “ breccia’ or 
“ petrosilex breccia,” being principally, usually almost wholly, 
composed of fragments of petrosilex cemented by a paste of 
the same rock more finely comminated. The breccia is often 
of a greenish color, and in not a few localities includes in both 
fragments and cement large amounts of what appears to be 
more or less perfect pinite, i.e, material of a light green or 
greenish-white color, which yields readily to the knife, affords 
water in the closed tube, and is somewhat unctuous, resembling 
serpentine in many of its piste: characters, and yet easily . 
west from Newton pee West Dedha am; many points in 
Hyde Park and the adjacent part of Dorchester Tintsonnit 
and Milton, between the Neponset River and Pine Tree Brook. 
The basins mentioned as holding the Primordial strata and 
the underlying breccia have been excavated from the ancient 
Huronian formation, which, in Eastern Massachusetts, consists 
mainly of the following lithological members: granite, binary 
and hornblendic; petrosilex, stratified and unstratified ; strati- 
fied and unstratified diorite; and quartzite. In these old erys- 
talline rocks we have the sources of all the materials observed 
in the conglomerate and breccia, pet excepting the pinite. In 
this connection, the most interestin uronian terrane is the 
petrosilex. For the sake of convenience, I here include under 
an 
true felsite. The physical iaueton between the true petro- 
silex and felsite, in Eastern Massachusetts, are not conspicuous. 
They both include exotic and indigenous varieties; and both 
present the same general range in textures, including, besides 
the ordinary compact and porphyritic forms, many different 
kinds of banded structure. Elvanite or quartz porphyry is 4 
common rock; but this belongs, of course, entirely to the acidic 
As a result of numerous chemical analyses, I fin 
that the petrosilex predominates, and is usually of red, brown 
or purplish tints; while the characteristic colors of the felsite 
are greenish, whitish and sometimes black. 
