1880.] 357 [Diller. 
Some of the rocks of the stratified group have been incorrectly 
named felsite. There is no true felsite belonging to the stratified 
group. The quartzite and slates are wholly distinct from the felsites, 
both in structure and origin. 
GRANITE. 
The term granite is here used to include all granitic rocks 
associated with the felsites. These rocks differ considerably in their 
external appearance and will afford a rich field for study. 
Mr. Crosby has represented the granite of West Medford as 
separated from that south of Spot-Pond by a broad belt of felsite. 
The felsite, as we have already stated, does not occur in the place 
represented by Mr. Crosby, and in its stead there is granite. North- 
east of Prospect Hill, in Malden, there is quite a large area of granite 
which is not represented on Mr. Crosby’s map. Another area occurs 
a mile further east along the Boston and Newburyport turnpike. 
The boundaries of most of these areas are very easily traced and 
some very distinct junctions with the felsites and stratified group 
have been observed. In by far the greater number of cases, however, 
the line of contact is covered. Whenever there are good clean 
exposures along the boundary of the granite, careful searching will 
result in the discovery of a plane on the one side of which the rock is 
granite and on the other side of which the rock is of a different kind. 
Near the west end of Long Pond in Melrose the granite contains 
distinct inclusions of the stratified group. ‘The stratification in the 
enveloped fragments is very evident. In many places, along the 
boundary between the granite and the stratified group, the latter con- 
tains distinct intrusions of the former. These dike-like masses of 
granite frequently envelop large angular fragments of the stratified 
group. The distinct line of contact between the two kinds of rocks is 
proof that the granite and stratified group are different formations 
and do not pass into each other by a gradual transition. The strati- 
fied group is undoubtedly of aqueous origin and the facts enumerated 
above, as Mr. Crosby and others have already shown, are conclusive 
evidence that the granite is eruptive. 
It must follow also that the granite in its present position is 
younger than the stratified group. 
1 Mr. M. E. Wadsworth informs me that the granite is distinctly eruptive at 
Swampscott, and that the rocks of that region are not correctly mapped by Mr. 
Crosby. 
