478 HENRY S. WASHINGTON 
objection may be met with the fact that such asymmetric lacco- 
liths are known, and are to be looked for in certain conditions of 
the surrounding strata.t Further, the presence of the coastal 
fault line and the Atlantic Ocean to the east is a sufficient explana- 
tion for the disappearance of a large part of the mass on this side.’ 
The irregularity of the quartz-syenite is a more serious objection, 
and is, perhaps, best explained by the admitted fact that the lac- 
colith must have been of a decidedly irregular shape, owing to 
the conformation of the strata into which it was intruded. It is 
possible, also, that considerable faulting may have taken place. 
The microscope shows that most of the rocks have been sub- 
jected to pressure, such as would be consequent on crustal 
movements. It must be noted that I am here using the term 
laccolith in a broad sense, as Cross and Pirsson have done to 
include ‘‘all thick lenticular (in this case elongated) masses which 
have domed up the strata, and have over the greater part of their 
area a roof of sediments’’3 (here largely disappeared through 
erosion, glacial, and otherwise). The actual presence of this last 
feature is not essential to the idea, since any cover may be 
removed by erosion without affecting the original character of 
the mass. 
It may also be remarked that, as far as can be seen, the 
course of differentiation would be the same whether, as in a true 
laccolith, the intruded magma bulged up the overlying strata, or 
entered an arch space formed otherwise.+ From the petrological 
standpoint the mechanics of the process are of secondary impor- 
tance. The chief point of my suggestion is that the differentia- 
tion was laccolithic and of a mass zx stfu, and not deep magmatic, 
and the rocks the results of successive intrusions. In the one 
™W. Cross: Fourteenth Ann. Rep. U. S. G. S., p. 236 ff, 1895. | PIRSSON: 
Eighteenth Ann. Rep. U.S. G.S., pp. 555, 581, 1898. 
?Mr. SEARS (Bull. Essex Inst., Vol. XXII, p. 16, 1890) notes the occurrence of 
Cambrian limestone at Jeffrey’s Ledge, in the Atlantic Ocean, about twenty miles east 
of Cape Ann. 
3 PIRSSON: @oc. cit., p. 581. 
4For an example of the latter cf. WATTS: Rep. Brit. Assoc. 1886, p.670 and Proc. 
Geol. Assoc., 1894, p. 341. 
