Diller. ] d64 [January 21, 
BRECCIA. 
The breccia is made up of angular and sub-angular pebbles, 
almost all of which are felsite. Those of granite and quartzite 
occur very rarely and in particular localities. Even in the Malden 
Highlands where the breccia is surrounded by “ basic felsite ” there 
are few if any pebbles of that felsite in the breccia. The fragments 
are commonly black, red or purple, and some are distinctly banded. 
They may be porphyritic or not, but almost all are very hard and 
flinty, differing markedly from the adjacent “ basic felsite.”’ The 
groundmass of the rock, or rather the paste in which the pebbles 
are embedded is usually light colored, non-porphyritie and quite 
compact. Sometimes the paste contains no pebbles and is very 
compact, closely resembling a light gray felsite. 
There is no other rock in this vicinity whose boundaries are so 
difficult to determine as those of the breccia. The reason for this 
difficulty will be found in the genetic relations of the felsites and 
breccia. 
North of Maplewood the breccia passes into a distinct sandstone 
and conglomerate. At the base of a hill a short distance north- 
east of Oak Grove Station, the breccia is associated with a red 
sandstone. Microscopic sections of these rocks have been made and 
show that they are distinctly sedimentary. 
The passage of the breccia into distinctly sedimentary rocks has 
been noticed at other places by a number of observers, and is 
sufficient evidence to prove that the breccia is of aqueous origin, 7. é., 
that it was formed as ordinary sandstones and conglomerates were 
formed, but its fragments were not so completely rounded. 
Near the corner of Pleasant street and Highland- avenue, Malden, 
is a gravel pit in which the sedimentary formation of breccia is nicely 
illustrated. At some time during the past, when the waves beat 
against the hillsides (ten to twenty feet above present high tide 
level) at that place, angular pieces of felsite were torn off and 
shingled against the steep rocky shore. The mass of fragmerits 
differ from breccia only in this, that the latter has been consolidated. 
It is evident that the felsites, fragments of which are found in the 
breccia, must be older than the breccia itself. We cannot, however, 
conclude from this, that all the banded and other silicious felsites are 
older than the breccia. On Marblehead Neck the breccia contains 
dikes of felsite, which must be younger than the breccia. The same 
