duced, with some modifications, from the map of Nantasket in 
the atlas of Plymouth County, 1879; while I am personally re- 
sponsible for the outlines of the central area, between the ( bounty i 
Road and railroad, and for the entire south shore of Weir River 
Day, Lyford's Liking and Strait's Pond. 
The general absence of roads or other artificial land-marks 
west of Hull Street and the County Road, and especially west 
of the railroad, and the fact that the hills and other natural 
features in this section were still unnamed, caused it to appear 
desirable, in the interests of concise and intelligible description, 
to assign names to the more important rock masses, marshes, 
ete. Of course it is not expected that many if any of the geo- 
logie and descriptive designations which appear upon the map 
and in the following pages will gain general acceptance ; and 
this is in no wise essential to their present usefulness. The 
aetual exposures of the hard rocks are so nearly continuous 
over the areas where they are indicated by colors on this map " 
that it has appeared unnecessary to represent the individual 
ledges or outerops; although this is virtually done for all the 
ledges in the marshes and below the high-tide line. And; ex- 
cept in the case of some of the fault-lines; the map may be 
fairly regarded as a plain record of actually observed facts, de- 
vold of theory. 
THE GRANITIC ROCKS OF COHASSET. 
This heading, in its broadest application, covers all the geo- | 
logical formations of Cohasset, except the dikes of diabase and | 
porphyrite and the drift deposits. The dikes, being essentially | 
similar in character and age to those of Nantasket will be most | 
conveniently described in that connection ; and since the super- f 
ficial geology forms naturally one continuous chapter for the en- | | 8 
tire area to which this paper relates, the drumlins, sand plains, 
ete., of Cohasset will not be taken up separately. But it appears 
best to introduce a general account, lithological and structural, 
of the granitic rocks of Cohasset at this point, because they form, 
