214 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the conglomerate. The weight of the evidence seems to the writer to- 
favor the idea that the melaphyr is effusive. Figure 6 represents a 
portion of the contact along the south side of the exposure. 
The Brighton, Brookline, and Newton areas have been included in 
a discussion centering on the question of effusive or intrusive origin. 
The main participants in the most recent phases of the controversy have 
been Crosby and Burr, the former upholding the effusive theory and 
the latter the intrusive. ‘The main arguments cited by Burr in defense 
of the intrusive theory are: (1) wherever contacts between the igneous 
rocks and the sediments occur the latter are penetrated by tongues of 
melaphyr which cut. across the bedding and display little sympathy 
with the stratification; (2) there is always a baked, discolored, and 
indurated contact zone in the sediments; (3) no pebbles, definitely 
determinable as melaphyr, occur in the conglomerates that appear 
to overlie the melaphyr; (4) the melaphyr occurs at varying horizons 
and in connection with both anticlinal and synclinal structures,— a 
feature quite in accord with the intrusive idea (Burr, b, p. 54-61). 
Crosby maintains on the other hand: (1) that dikes of such width 
(3,000 feet), without holocrystalline structure but with well-marked 
amygdules, cannot be regarded as probable; (2) that in the area. 
between Newton Upper Falls and Newton Highlands several bands 
of melaphyr appear interbedded with the conglomerate and that these 
bands are solid, homogeneous, and holocrystalline toward their south- 
ern borders but more slaty, amygdaloidal, and scoriaceous northward; 
(3) that these bands are covered with conglomerate which is crowded 
near the contact with angular fragments like the melaphyr, but becomes 
practically free from melaphyr masses within two yards of the contact; 
(4) that the melaphyrs of Boston are essentially unlike known dikes 
or sills; (5) that the irregular contacts may be explained as sedimen- 
tary contacts with the lava surface; (6) that the supposed baking is 
the result of silicification from the chloritization of the melaphyr; (7) 
that the reddening is caused by the impregnation of the sediments by 
the ferruginous materials of the melaphyr (Crosby, 0, p. 324-326). 
Modifying to some extent his former views, Crosby supports Burr's 
contention that the melaphyrs are not confined to one horizon (ibid., 
p- 326). 
The writer has visited many of the localities described by Burr and 
has also had the opportunity of examining his specimens and slides. 
As regards the Brighton area he is in full accord with Burr’s conclu- 
sions. The mere fact that it is unusual for heavy bodies of intrusive 
rock to lack holocrystalline structure and to possess amygdaloidal 
y 
Ay- 
