The Geology of Hingham. 45 



mately almond-shape in their outline. These cavities, how- 

 ever, may be entirely wanting, when of course the name amyg- 

 daloid loses its significance. Moreover, rocks of a different 

 composition have sometimes the same amygdaloidal structure. 

 The name now applied to the rock by geologists is Melaphyr, 

 and nowhere does it present itself in its typical and varied char- 

 acteristics more advantageously for observation and study than in 

 Hingham. The composition is the same as that of Basalt, which 

 has as its essential elements, augite, magnetite, and titaniferous 

 iron, but often containing a triclinic feldspar and other minerals, — 

 the only difference being apparently the result of a change of 

 some of the constituents by decomposition. Here it is found 

 beautifully amygdaloidal over extensive areas, the amygdules 

 being filled with minerals of several species which are sometimes 

 arranged in concentric bands, the most common being epidote, 

 quartz, chlorite, and calcite. At one locality, on land bordering 

 Unit's Cove, there is an exposure of melaphyr, forming an escarp- 

 ment on the slope of a hill, which is quite dark in color and in 

 portions free from amygdules, and where these occur they are of 

 calcite. This is found in the immediate neighborhood of other 

 melaphyr, full of amygdules containing the various minerals men- 

 tioned as common in the rock. 



The best exposures for the study of melaphyr may be found at 

 the northeast part of the town along the shore of Rocky Neck, 

 on the northeasterly slope of Squirrel Hill, Lincoln Street, and at 

 Huit's Cove. At all these places the amygdaloidal rock is abun- 

 dant, and specimens of much beauty can be easily obtained. In 

 the amygdaloidal melaphvrs of Rocky Neck fine red jasper and 

 vellowish white epidote occur, both in nodules and in veins. 



CLAY SLATE OF THE SLATE SERIES. 



This slate, which forms a great body resting with apparent con- 

 formity over the rocks of the conglomerate series, has a thick- 

 ness of over one thousand feet, and undoubtedly is spread, as indi- 

 cated on the maps, over a great area of the town toward Weymouth 

 River. Its exposures are, however, not numerous, as the drift of 

 the glacial period covers it from observation. It shows itself on 

 the border of Weymouth River at Deal's Cove, and also at Huit's 

 Cove. At the south side of the latter it forms a point of land 

 which extends into the water. Here it is well-jointed, and the 

 lines of stratification are distinctly perceptible. The dip is west- 

 erly, and the inclination about 60°. On the north shore of the 

 cove it appears associated with conglomerate and melaphyr, and 

 portions of it show clearly lines of cleavage which are not often 

 manifest at the exposures of slate in Hingham. 



In a region where the rock formations have experienced great 

 disturbance, as in Hingham, the dip of the strata varies very 



