MUSEUM OF COMTAKATIVE ZOOLOGY. 177 



Pond in Melrose. Although tho locality is small, it embraces a variety 

 of fine-grained, red, argillaceous rocks, sandstones, and a very coarse con- 

 glomerate composed almost wholly of pebl)lt's of quartzite from the 

 stratified group. 



In the base of a small hill a short distance northeast of Oak Grove 

 station, on the Boston and Maine Railroad, the fragmental rocks of this 

 group are well exposed. They extend into the base of Prospect Hill, 

 and on the opposite side of the valley are exposed near the base of 

 the Maiden Highlands. Within the Highlands there are two small 

 areas of tufas, one on each side of Highland Avenue along the Malden- 

 Medford line. The conglomerate of West Medford, which is well de- 

 veloped along Purchase and Mystic Streets, resembles to a considerable 

 extent some parts of the Koxbury conglomerate ; but Mr. Crosby is most 

 likely correct in connecting it with the fragmental rocks so intimately 

 associated w'ith the felsite. 



Within the felsitcs north of the stratified gi'oup we have found only 

 two small areas which, as it seems to us, are of sedimentary origin. One 

 of the patches lies upon the first hill north of Oak Street, a short dis- 

 tance west of Nahant Street (Main Street), Wakefield, and the other 

 is upon Candle-wood Hill, northeast of the Stoneham station on the 

 Boston and Maine Railroad. It is very probable that a number of areas 

 of sedimentary rocks have escaped our notice, but we feel sure they do 

 not occupy the large areas over which they have been represented to 

 extend. The very porphyritic felsite occupying the region lying between 

 Long Pond, Saugus, and the Maiden Highlands contains, as we have 

 already stated, many pebbles of other felsites, and some of granite, but, 

 like that at Red Rock, Lynn, it is by no means of sedimentary origin. 



We have elsewhere * shown that some of the felsites are younger than 

 the fragmental rocks so intimately associated with them, and it remains 

 in this connection to point out the facts upon which this inference 

 is based. 



In the conglomerate about a fourth of a mile north of Cliftondale 

 station there is a dike of pinkish felsite which is clearly eruptive 

 through the fragmental rocks of the same locality. A similar phenome- 

 non may be seen north of Oak Street, Wakefield, where a distinct tongue 

 from the black-edged dike penetrates the adjoining fragmental rocks. 

 The best locality, however, for observing the relations of these rocks is 

 southeast of Swain's Pond, where the porphyritic felsite not only pen- 

 etrates in the form of small, irregular dikes the fragmental rocks, but 



* Pioc. Bost. Roc. Nat. Hist., Vol. XX., p. 364. 



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