340 H. N. EATON 
wanting. From the fact that the slate is underlain by limestone 
in many places along the belt it would seem that the maps of the 
Second Geological Survey give the correct interpretation. The 
apparent unconformable overlap of the Hudson River slate upon 
the Cambrian formations is a point worthy of further study. 
MESOZOIC ROCKS 
Triassic System; Newark Series 
The Newark is undifferentiated on the map. East of Cushion 
Peak basic igneous rocks of the diabase type form the southern 
boundary; westward the Newark rocks adjacent to the mountain 
consist of red basal conglomerate with quartzite pebbles and sand- 
stone dipping gently south. The southern base of South Mountain 
was locally part of the northern border of the Triassic Sea. 
Structure 
Rogers! attributes the width of outcrop of the quartzite south of 
Newmanstown to “‘the presence of two or three anticlinal flexures.”’ 
It was impossible either to verify or disprove this view during the 
present investigation. In the dense woods of oak and chestnut 
west of Eagle Peak outcrops are few and the above statement 
would seem to imply a hasty generalization from very meager 
data. One outcrop on the western slope of the mountain gave a 
strike N. 60° E., and a dip 70° N.W. Mr. J. H. Eby,? a min- 
ing engineer formerly of Mountville, Pa., states that the quartz- 
ite at Eagle Peak and farther west dips into the mountain. 
Whatever the truth may be concerning any minor undulations, 
the northwestern slope of South Mountain probably represents a 
steep upbuckling of the quartzite decreasing in dip toward the 
valley, with a possible slight overturn near the gneiss. 
From Robesonia eastward the structure becomes more apparent, 
coincident with the narrowing of the quartzite outcrop. A short 
distance south of the Robesonia iron furnace the quartzite was 
observed to dip south into the mountain at an angle of 47° within’ 
1 Op. cit., 202. 2 Personal letter. 
