250 



J. F. KEMP — ROCKS OF THE EASTERN ADIRONDACKS. 



logical Survey. All run in a direction of about N. 60° E. and cut the 

 strike nearly at right angles ; but as this varies from N. 10° E. to N. 40° 

 W., or even more, the statement is not always strictly true. 



Figure 3 represents a cross-section through the large ophicalcite quarry 

 of Mr Treadway, half a mile north of the town, and through a low^er 

 lying white limestone, well opened for furnace stock. It shows below 

 this, after a concealed strip, mica-schist, black garnetiferous hornblende- 

 schist, more white limestone and black schist, and finally the great in- 

 trusion of gabbro at the lake. 



OPHICA LCIT E 



N i)M E 



Figure 3.— Cross-section at Ophilcalcite Quarry, near Port Henry, New York. 

 The arrows indicate the strike in plan. 



The general dip is a flat one of about 20 degrees, as a maximum, to 

 the west. Over the ophicalcite is light gray gneiss, with additional 

 ophicalcite showing higher, but farther south. Still, dips are quite un- 

 certain quantities in these dynamically metamorphosed beds, and are 

 mostly, for individual beds, pressure-effects as shown by sheared inclu- 

 sions. Where there is a change from one kind of rock to another a con- 

 tact-dip, however, is developed which is worthy of the geologist's serious 

 consideration. The topography indicates that there is a great fault to 



FAULT? 



N t>M.E; 



Figure 4:.— Cross-section one Mile north of Cross-section represented in Figure 3. 



the west which intervenes between these exposures and the Bald Peak 

 ridge of gneiss and gabbro. The fault is a continuation of the one met 

 in the Cheever mine, as shown in figure 5. 



Figure 4 represents a section about a mile north of and parallel with 

 the cross-section indicated by figure 3. It shows much the same suc- 

 cession, except that the limestone appears on the lake-shore instead of 

 gabbro, and at the west end the dips are much steeper. In addition, 300 

 feet of gneissic rock were cut in explorator}^ drill-holes with the diamond 

 drill in searching for ore south of the Cheever mine. The rock on the 



