GEOLOGY : SOUTH SHORE. 23 



from the granite, which is thus proved to underlie the volcanic 

 rocks and conglomerate. 



2. The Nantasket ledges west of Hull street. 



Soute. — The chief points of interest in this area are reached most 

 readily from Nantasket station by walking south along the railroad to 

 Great hill on the extreme south side of the harbor. 



As we approach Great hill, which is the bold and isolated em- 

 inence on the west of the tracl?, we have on the east side the 

 beginning of an interesting north-south section, extending over 

 Crescent hill (opposite Great hill) to Marsh island in the Weir 

 river marshes. This section consists, from below upward, of the 

 Third Conglomerate, Second Melaphyr, Fourth Conglomerate, 

 and Third Melaphyr. The contacts are admirably exposed and un- 

 mistakably contemporaneous. The section is broken by numerous 

 east-west faults, repeating the beds to a considerable extent ; and 

 this faulted zone is bounded on both east and west by important 

 nortli-south faults. The easternmost fault separates it from Mela- 

 phyr plateau, in which these two beds of basic and amygdaloidal 

 melaphyr are situated, brought together in one broad and contin- 

 uous outcrop. 



We next cross the marsh westward from Great hill to Granite 

 plateau and the shore of Weir river. Scattered over the granite, 

 which is clearly the fundamental rock for this stratified series, are 

 patches (outliers) of the first or basal conglomerate ; and the 

 roots of this conglomerate may be seen filling original cracks and 

 fissures in the granite, and forming one type of sandstone dikes. 

 Proceeding north from Granite plateau to Granite point and Cliff 

 plateau, the basal conglomerate is found to be overlain by the First 

 Melaphyr, a compact, non-amygdaloidal variety, quite distinct in 

 character from any other Nantasket flow. It is characterized in 

 ■part by segregations of bright red jasper; and this feature is 

 common also to the underlying and overlying First and Second 

 Conglomerates. The section is particularly clear in West Poi"phy- 

 rite hill, northwest of Cliff plateau, where we have in regular 

 sequence, with the contacts well exposed, the First Melaphyr, 

 Second Conglomerate and a heavy bed of porphyrite. North of 

 this hill, and separated from it by a profound fault, is Melaphyr 

 peninsula, affording an exceptionally fine section of a typical but 



