ADIRONDACK MAGNETIC IRON ORES 125 



name from their extensive occurrence along the Saranac river in 

 this section. 



In his report " Geology of Clinton County," Cushing describes as 

 belonging to a separate type, a.silicious gneiss, resembling quartzite 

 in appearance, but composed of microcline and quartz, with garnet 

 and a mineral that corresponds optically to sillimanite. It occurs 

 along Trout brook which enters the Saranac at Russia. From its 

 composition he is inclined to consider the rock a sedimentary 

 derivative and he further suggests that there may be a belt of 

 related gneisses and crystalline limestone within the drift-covered 

 valley. The exposures are insufficient to establish the extent of 

 the sedimentary or Grenville rocks, but it is probable that such a 

 belt exists. Further evidence confirming this view was found by 

 the writer near Clayburg where a biotite schist is exposed along 

 the west bank of the Saranac river. The schist has been injected 

 by granitic materials, though its characters are plainly those of 

 the Grenville series, shown by its crumbling well foliated texture, 

 pyritic inclusions and variation of composition across the strike. 



Small areas of gabbro are found at two localities in the district. 

 The largest exposure is just north of Clayburg and is about 50 

 yards wide; the second outcrop is west of Russia on True brook. 

 They occur as dike intrusions in the Saranac gneisses. 



Diabase dikes are numerous. Cushing has listed 26 within the 

 townships of Saranac and Black Brook and several more occur in 

 the mines that have not been recorded. They are the latest of the 

 recognizable igneous rocks. 



Of the sedimentary rocks the Potsdam sandstone composes a 

 part of the surface geology of the district, occupying a large area 

 in Saranac township east of the river. It is not exposed 

 anywhere in the vicinity of the ore bodies. 



Averill mine. Near Dannemora village are the Averill, Ellis, 

 Fairbanks and Dannemora mines, all of small size. They lie on the 

 slopes of the high ridge which forms the north side of the Saranac 

 valley and of which Dannemora mountain marks the culmination 

 in this part. 



The Averill mine is the largest of the group. The ore body is 

 first encountered a few hundred feet southwest of the State Prison 

 and can be traced in a northerly direction for 1000 feet. It is 

 inclosed in a basic hornblende -biotite gneiss, the ore itself consisting 

 of streaks and bands of magnetite alternating with the materials 

 of the wall rock. The latter is cut by reddish granite of which 

 there is a large exposure on the hill back of the prison that has 



