324 The American Geologist. ^-i^y, luoi 
CORRESPONDENCE. 
Are the Amygdaloidal Melaphyrs of the Boston 
Basin Intrusive or CoNTEMPORANEOusf — The recent pa- 
per by my friend, Henry T. Burr on the "Structural Rela- 
tions of the Amygdaloidal Melaphyrs in Brookline, New- 
ton and Brighton, Mass.,"* is, in the main, a criticism of my 
view that the melaphyrs of this area, as of the other parts of 
the Boston Basin, are chiefly contemporaneous, and of an un- 
published map by Woodward in which that view is embodied. 
I have not claimed that the melaphyrs are wholly contempo- 
raneous, recognizing that they must be intrusive at some 
points, since the magma necessarily reached the earth's sur- 
face before it could play the role of an effusive ; but in the 
area which he has studied. Mr. Burr finds all the melaphyrs 
to be intrusive. His argument rests largely upon the evi- 
dence of the contacts, which are found to be, without excep- 
tion, where clearly exposed, igneous. Details which appear 
to support this thesis are made the most of ; but broad, funda- 
mental facts which tell strongly against it have not been duly 
considered. No attempt is made to show that none of the 
irregular contacts supposed to be igneous could be as well 
explained as due to the covering by sediments of the cracked 
and scoriaceous surface of a submarine flow ; or that the sup- 
posed baking of these overlying sediments is never silicification 
accompanying the chloritization of the melaphyr. The ori- 
eiitation of feldspars in conformity with the contact is em- 
phasized, although this feature belongs also to the free sur- 
face of a flow, and not alone to its igneous contact with an- 
other rock. Notwithstanding the title of his paper, as quot- 
ed above, our author takes absolutely no account of the very 
prevalent amygdaloidal and scoriaceous textures of the 
melaphyr and his sections show dykes of melaphyr 
from 500 to more than 3,000 feet in width. He starts 
out by noting that the melaphyr and the trap dikes of the dis- 
trict are, petrographically, hardly distinguishable ; but does 
not attempt to show why, if the trap and the melaphyr are 
both intrusive, a three-thousand-foot dike of the melaphyr 
should be throughout amygdaloidal, scoriaceous or aphanitic, 
while a three-foot dike of trap is holocrystalline and homoge- 
neous. If these masses of melaphyr really are dikes from 
500 to 3,000 feet wide, it would be very interesting to know 
where and how they terminate ; and certainly a fissure 3,000 
feet wide filled with basic magma at a level in the crust per- 
mitting it to solidify with aphanitic and vesicular textures 
could not have failed to gush effusively at the surface; but 
no suggestion is oft'ered as to what has become of this effu- 
* Bull. Mu6. Comp. Zool., Geol. Series, 5, 53-69. 
