•ROSS-SEfTIONS AT PORT HENRY LOCALITY. 



251 



surface is a gneiss with disseminated magnetite, and some thin beds of 

 ore were met 800 feet below the surface. Ex])osurcs are not continuous 

 and the po^^8ibiHty of isoclines is not to be overlooked, but it seems reason- 

 able to til ink that there are from 1,000 to 2,000 feet ol conformable strata 

 in this section. 



Figure 5, representing the next cross-section half a mile north, is based 

 on the Cheever mine, and in its underground outline is indebted to Mr 

 B. T. Putnam'::, map,* omitting a number of small faults, with throws of 

 ten feet and less, which would not show on the scale. There is at the 

 east end an enormous gabbro intrusion which cuts off the lower lying 



X X X X y X K "Tk k^^^s 

 XXX><>X'<,XXX xfe^ 



Xxxxxxxx*^ x-^-^ 



XXX XXX XX XX 



N to E GABBRO 



Figure 5.— Cross-section at Cheever Mine. 



limestone indicated in figure 4 and curls up the edges to a high dip. 

 From this they flatten out to the westward, being checked as to their 

 accuracy by the mine-section which is drawn from surveys. Fifty feet 

 below the ore, whose foot-wall is gray pyroxenic gneiss, schistose and 

 then massive gabbro appears, while over it is gray pyroxenic gneiss pass- 

 ing into hornblendic gneiss and crystalline limestone, and finally at the 

 extreme west ophicalcite. A fault was" met in the mine which cut off 

 the ore as with a knife and brought the workings against a gabbro wall 

 upon which the ore had slipped down. The topography also indicates 



3W OPMiC. SCMISTS AMD ONEISSCS (\J £^ 



FiiJi'KK 0. — Cross-section in Moriah Township, cast of Spragucs Corners. 



the fault, for the lower hills at the mine are succeeded by a flat meadow 

 where exposures are concealed, but further south a small outcrop is 

 gneissoid gabbro, and fresh normal gabljro was found on the dump of 

 the mine nearest the fault. 



From these sections it is clear that white, coarsely crystalline, gra})hitic, 

 limestone, together with gneissoid and schistose rocks, among which black 

 garnetiferous. hornblendic varieties are most j)rominent, make uj) the 

 lower and middle portions of the series, and that the oj)lii('ah'ite aj)})ears 

 toward the top. The sections also show (and the con(;lusion is corrob- 



*8ee Tenth Census, vol. zv, p. 113. 



