70 
features of this belt of ledges are readily explained by one bed 
of conglomerate between two very similar flows of melaphyr, 
with only such dislocations as are actually seen ог may be rea- 
sonably inferred, until we come to the conglomerate underlying 
the lower melaphyr south of dike 25. This is a partial expo- 
sure only of a lower and older conglomerate which does not 
appear elsewhere in the section. 
Although the transverse faults of this block are frequently re- 
versed in throw and compensating 
85 
the northerly throw clearly 
prevails, the sum of all the displacements giving 161 feet to 
the north and 71 feet to the south. Hence the entire series is 
equal to one northerly slip of 90 feet. 
Melaphyr Plateau.—This rectangular block of melaphyr 
is sharply defined by the bounding fault lines and escarpments, 
and may be regarded as a very characteristic feature in Nan- 
tasket geology. With the exception of the small patch of con- 
glomerate on the western edge, it consists throughout of the 
most typical, basic, green variety of melaphyr, with frequent 
highly amygdaloidal layers. The flow-strueture is very perfect 
at many points, and shows that the sheets or flows are still 
nearly horizontal, with slight undulations to north and south and, 
perhaps, a very gentle general dip to the southeast. The facts 
already stated in connection with the mass of conglomerate pro- 
jecting into the western edge of the plateau indicate that the 
plateau embraces both of the flows of melaphyr observed in the 
Crescent Hill section. The lower flow forms the northern bor- 
der of the plateau, or that portion north of the conglomerate ex- 
tension ; while all the remaining area, or fully three-fourths of 
the whole, must be referred to the upper melaphyr. The con- 
glomerate, which normally separates the two flows, has been en- 
tirely cut out of the section, so far as the surface development 
is concerned, by the oblique strike faults. At the extreme east- 
ern end of the plateau there are indications, in the form of thin 
outliers of sandstone, that the upper melaphyr was also for- 
merly covered by conglomerate. It will appear later that this 
