BURR: MELAPHYR OF BROOKLINE, NEWTON, AND BRIGHTON. 55 



1. The Lack of Melaphyr Pebbles in the Conglomerate. — The 

 melaphyr appears to be overlain by a considerable thickness of heavy 

 conglomerate. This is particularly true of that in the Brookline area, 

 where it occupies the centre of an anticline and is surrounded by the 

 coarse basal beds of the conglomerate, dipping away from it in all direc- 

 tions. Heavy sediments, such as these, must have been deposited in 

 shallow water, within the zone of wave action. It is not easy to see 

 how they could have been formed without including some fragments of 

 the underlying rock. With this in view the conglomerate has been 

 carefully examined. Few pebbles of basic character have been found, 

 none referable to the melaphyr. 1 Such evidence is of negative charac- 

 ter, and is, therefore, not conclusive, but it has some considerable 

 value. 



2. Evidence from Contacts. — The zone of contact between the 

 melaphyr and the sediments is evidently a zone of weakness, for its 

 place is generally occupied by swamps and other low places. Actual 

 contacts are, therefore, not often seen. On Newton Street, Brookline, 

 (Plate 2, Loc. 1), nearly opposite the end of South Street, is an irregu- 

 lar mass or tongue of melaphyr nearly surrounded by conglomerate. 

 This mass cannot be traced far in any direction, but is presumably con- 

 nected in some way with the main melaphyr mass to the west. It is 

 seen in contact with the conglomerate at several points. It cuts the 

 latter in a very irregular way, and without regard for bedding or 

 structure. It is certainly not a flow nor even an intrusive sheet. It is 

 best regarded as an irregular tongue or offshoot from the main melaphyr 

 mass. The rock at this point is the typical melaphyr and is not to be 

 confounded with the later traps. 



Farther westward, on the south side of Brookline Street (Plate 2, 

 Loc. 2), the melaphjT is again exposed in contact with conglomerate. 

 The melaphyr at this point is not over one hundred feet wide and is 

 flanked by conglomerate on both sides. The only contacts exposed are 

 on the northern side of the melaphyr. This would be the lower side if 

 the rock represented a flow. This contact is unmistakably igneous. 

 The hard sediment has been fused, in contact with the igneous rock, to 

 an homogeneous red mass which has the appearance of felsite. It is 

 unfortunate that the southern contact is not shown. It is, however, 

 hardly possible that the melaphyr can be a flow, for it cuts the sedi- 

 ments vertically while the latter have a prevailingly gentle dip to the 



1 Professor Crosby ('89, p. 10), however, states that the conglomerate contains 

 fragments of the melapliyr. 



