223 



finally passes gradually into brownish slate, very similar to 

 that on the north of the conglomerate, but with a gentler dip 

 and less perfect cleavage ; it is also more distinctly laminated. 

 If the slate north of the conglomerate lies in a syncline, as con- 

 jectured, then the conglomerate itself forms an overturned and 

 denuded anticline ; a view which is confirmed by the exceed- 

 ingly coarse texture of the middle portion of the conglomerate 

 belt, the pebbles becoming gradually smaller toward the slates 

 above and below. 



The slate overlying the conglomerate on the south continues 

 for four hundred feet, the dip gradually diminishing from 40° 

 to 15° ; and then the section is concealed for about five hundred 

 feet, and, after a few feet of slate similar to the last, and dip- 

 ping south 20°-30° ( ?) , for four hundred feet more. Following 

 this are two hundred and sixty feet of the same slate, overlaid 

 conformably by one hundred feet (traverse measure) of a green- 

 ish-white, or grayish, massive slate. The bedding of this variety 

 is much disturbed, the dip varying from 30° to 60°, but remain- 

 ing always southerly. Beyond this the section is concealed to 

 near the south shore, where the conglomerate reappears with a 

 high dip S. 20° E. The same conglomerate outcrops on the 

 eastern end of Moon Island, where it is intersected by endo- 

 genous quartz, and holds arenaceous beds, which show a dip 

 S. 20° E. 70°— 80°. This rock, here, as on the south shore 

 of Squantum and in the vicinity of Milton Lower Mills, is on 

 the northern border of the Rainsford Island synclinal. The 

 west end of Moon Island is probably slate. The slate on the 

 north side of Squantum is not shown on the map. 



The rocks of the Neponset and Squantum belt probably occur 

 on Long Island, under the drift, and, possibly, form the foun- 

 dations of Gallop and Lovell's Islands. Green Island and the 

 Calf Islands are about on this line. These are slate ; and, as 

 already shown, this rock may be expected to predominate in 

 this direction. 



The West Roxbury and Dorchester Synclinal. — North 

 of Milton Lower Mills the dip of the conglomerate changes to 



