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



orated along the lake-shore by the contacts of gabbro and limestone) 

 that the gabbro has been intruded through the limestone. Subsequently 

 great pressure has operated on both, and has made the gabbro strongly 

 gneissoid in places, though leaving unaffected, massive portions, and has 

 wound the limestone around it and detached fragments of it near the 

 contacts. 



Figure 6 represents a section in western central Moriah township five 

 miles from the preceding one and on the other side of several ridges of 

 gneiss. The usual black hornblendic schists and limestones appear at 

 the base. The lowest member is a black hornblendic gneiss, which 

 becomes more feldspathic and quartzose in proportion to its remoteness 

 from the limestone. The highest lime-rock found is ophicalcite, as before, 

 but over it (unless there is a repetition from faulting, of which there is 

 evidence) in a succeeding hillock lies hornblendic schist and gneiss, and 

 on the last hill of the section there is a steep fault-scarp and massive 

 gneiss. Below the limestones are massive gneisses also. 



The characters common to these sections are important stratigraph- 

 ically and have a bearing on the origin of the rocks. The black horn- 

 blendic schists are quite invariably met all through the region and in 

 the same relations with the limestones. The latter are not thick, but 

 rather in lenticular beds rarely over 50 feet across, but, considered as 

 a whole, of great persistence. They are never pure limestone, but always 

 contain bunches of silicates. The ophicalcites, up to about 50 feet as a 

 maximum, are near the top of the series, but are quite irregular in 

 character and may fail entirely. 



Petrography and Mineralogy — The Limestone. — The typical limestone 

 is quite pure calcium-carbonate, as indicated by analyses at the Port 

 Henry furnaces. Twinning parallel — 2 R is invariably present, indicat- 

 ing former pressure, as already stated. Almost always scales of graphite 

 are scattered through it, and likewise small tables of phlogopite, irregular 

 quartzes and occasional little prisms of apatite. Disseminated coccolite 

 appears, but outside of the ophicalcite areas it is not common. Aside 

 from this, there is little worthy of note. The bunches of silicates, which 

 vary from small knots through snake-like stringers to great "horses" 

 from 25 to 50 feet thick, are more varied and interesting. In them there 

 has been detected graphite, pyrrhotite, magnetite, fluorite, quartz (usually 

 rose), rutile, apatite, plagioclase, black and brown tourmaline, biotite, 

 phlogopite, muscovite, hornblende, pyroxene, titanite, scapolite, garnet, 

 zircon and woUastonite. 



The general mass of a silicate inclusion, as shown by the microscope, 

 is a granitic or dioritic aggregate of plagioclase, quartz and hornblende 

 in rather coarse crystals, usually from 5 to 10 millimeters or more across. 



