212 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
have been the subject of some diversity of opinion. Professor Wolff 
has described the melaphyr as a great dike. He states that at the west 
end of the outcrop, on the south side, the junction of the melaphyr 
with the conglomerate and red sandstone is very irregular; large and 
small tongues of the dike penetrate into the conglomerate, the latter 
rock striking N 60°-80° W and dipping 70° S. The junction 
between the two rocks, he says, is sharp and well marked and the 
dike seems often amygdaloidal near the contact. Sections of the 
latter show that the dike is composed of a mass of small feldspars, 
showing a beautiful fluidal arrangement, while they are often bent 
when in contact with the line of the conglomerate. On the north 
side there is a fine vertical exposure where the rock is seen to stand 
almost vertically, the dike cutting the slate and conglomerate a little 
irregularly but nearly parallel with the strike (Wolff, p. 231-232). 
Professor Crosby, on the other hand, advocates the idea that the 
melaphyr is a flow. He maintains that the amygdaloidal and scori- 
aceous character of the upper part of the rock and the unsymmetrical 
section of the melaphyr are normal for a flow but abnormal for a dike. 
The highly but minutely irregular form of the upper contact, the 
compact and fluidal texture of the melaphyr near the contact and the 
abundance of the debris of the melaphyr in the base of the overlying 
conglomerate, while such debris is lacking in the underlying conglom- 
erate are adduced as further evidence of the effusive nature of the 
rock (Crosby, n, p. 494). The greater irregularity of the south con- 
tact of the melaphyr is noted by both Wolff and Crosby. Since the 
rock on both sides of the melaphyr is conglomerate of much the 
same character, it would seem, if the melaphyr were a dike, that both 
north and south contacts would have approximately the same degree 
of irregularity; yet there is a distinct difference in this respect. The 
amygdaloidal character of the melaphyr near the southern contact 
is noticed by both observers. While no general law can be stated, it 
may be said that such a characteristic is unusual for a dike but may 
well be expected in the case of a flow. The fluidal arrangement of 
the feldspars and the bending of the latter near the contact are both 
characteristics suitable for a dike, yet flow structure is often a well- 
marked feature of effusive rocks and it might well be that feldspars 
caught in the zone between the slower moving surface of the grad- 
ually congealing rock and the more rapidly moving interior would 
become bent or distorted. The occurrence of melaphyr debris in the 
conglomerate on the south, and the absence of such components in the 
conglomerate on the north are strong points in favor of the effusive 
, 
