81 
melaphyr at one point, rises so abruptly from beneath the mel- 
aphyr on the north as to suggest an intervening fault, which is 
indicated on the map, with the downthrow to the north. Layers 
of sandstone in the eastern end of this ridge show the usual 
easterly dip. The contact between the basal conglomerate and 
this northern patch of melaphyr is clearly exposed along the 
brink of the cliff and in the gorge formed by dikes 66, where the 
dip is southeast perhaps 10°; and it can be traced quite around 
the west end of the melaphyr, which everywhere plainly over- 
lies the conglomerate. The northern patch of melaphyr, like 
the southern, is overlain on the southeast by a thin eap of the 
second conglomerate, this upper contact being parallel with the 
lower. The normal succession of all the rocks in Cliff Plateau 
is clearly exhibited in the accompanying section. 
W. Clif Plateau. Dikes бб. E. Porphyrite Hill. E 
ERES: ] ы 
TRARA j SENS KI GANZ FOU 
Granite, Conglomerate, Мару". ` Porphyrite. 
Fic, 10.— SECTION FROM GRANITE POINT ACROSS CLIFF PLATEAU AND East 
' 
PonPHvRITE HILL. SCALE, I INCH = 400 FEET. 
East Porphyrite Hill. — This hill, which forms the promi- 
nent northeast angle of the western area, is separated from Cliff 
Plateau by the group of north-south dikes (66) and the depres- 
sion or gorge due to their erosion. It is surprising to find that 
these repeated fractures are accompanied by no appreciable dis- 
placement ; but the basal conglomerate, the melaphyr, and the 
second or overlying conglomerate can all be traced across the 
dikes without the least slip (Fig. 10). The basal: conglomerate 
just barely shows at the base of the cliff on the east side of the 
dikes and does not reappear beyond, the easterly slope of all the 
beds being very noticeable. The melaphyr can be followed 
OCCAS. PAPERS В. S. N. H. IV. 6. 
