280 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The second, and next most important occurrence begins, as can be 

 seen from the general map, at a point a httle north of Fox Hill and runs 

 in a southwesterly direction with a width of at least 500 feet for one- 

 half mile, or as far as Cedar Rock. Beyond this point a heavy mantle 

 of drift makes it impossible to say positively whether it extends 

 further in this direction or not, but it probably does, since as Professor 

 Crosby has pointed out, outcrops of the same rock occur further west 

 beyond Randolph Avenue. The southern and more elevated contact 

 with the porphyry is exposed at several points and it appears to be a 

 nearly straight line with minor irregularities. The northern contact 

 is unfortunately unsatisfactory. At one point Professor Crosby 

 states that it is in igneous contact with slate, but the extremely altered 

 condition of the exposures renders their study of little value. The 

 changes in the porphyry along the southern contact are, as has been 

 noted earlier, more suggestive of the contacts exposed at the eastern 

 end of the Pine Hill mass than that about Wampatuck Hill, although 

 the coarsening of the porphyry is not so marked. As the granite is 

 exposed only a very short distance north of what must be the northern 

 contact of the aporhyolite near its eastern end, the intervening 

 porphyry zone must be a thin one. From these facts, and from the 

 generally massive character of this mass of aporhyolite, it is thought 

 that the southern and more elevated contact represents a deeper zone 

 than that exposed about Wampatuck, l)ut more elevated than that on 

 the eastern side of Pine Hill; and also that if the contact was exposed 

 along the northern side it would be like that east of Pine Hill, just as 

 in the adjoining Pine Tree Brook area the slate contacts are the same 

 in character as those in the northern part of the Pine Hill tract, viz., 

 of the deeper level type. 



The third mass of aporhyolite occupies the northern top of Heming- 

 way Hill, as shown on the map. It is an elongated mass of no great 

 width and shows the same contact phenomena with the porphyry as 

 those found about Wampatuck Hill, except that there is perhaps 

 rather more brecciation of the porphyry, particularly near the north- 

 ern end of the hill. A marked flow structure with taxitic structure 

 characterizes a part of the exposed portions and the rock generally 

 appears like that on Wampatuck and Pine Hill. 



Megascopic characiers. — The prevailing color of the aporhyolite is a 

 dark reddish-brown or purple. Locally, where it has suffered from 

 strong surface weathering, it becomes whitish with brown rust spots. 

 In places it is an almost perfectly dense, structureless rock though it 

 usually shows a few small rectangular feldspar phenocrysts and less 



