r42 NEW YORK STATE MUSEIUM 



than the anorthosite, thue falling In line with the detailed obser- 

 vations already set forth. 



Section from Tupper lake to Rollins pond, N. Y. C. & H. R. R. R. 



The rack about Tupper lake is augite syenite, but anorthosite 

 is reached within 3 or 4 miles to the north and east, with no other 

 rock interyening, so that it was hoped that traverses from one to 

 the other would disclose outcrops which would give the clue to 

 the time relations. There are but two convenient lines of 

 section. 



For the first 3^ miles from the depot at Tupper Lake Junction 

 there are no rock cuts along the railway, but occasional ledges 

 are found in the woods within ^ mile of the track. These are all 

 of a greenish or brown gneiss which Ls clearly referable to the 

 augite syenite, but the outcrops are of the uneatisfactory sort 

 which prevail in the woods. At 3J miles is a low rock cut of 

 meager dimensions which furnishes however fresh material (906). 

 The rock must be classed with the augite syenite, though a 

 variant from the type in that it is somewhat more basic, with 

 extra large content of ferro-magnesian silicates for these rocks, 

 containing some 30^ of them instead of the 15^ to 20',^ of the 

 normal rock. The difference is but slight, however. Much mag- 

 netite and garnet are present, considerable augite and horn- 

 blende, less bronzite, a little biotite, and the usual zircon and 

 apatite. There is some ^^ of quartz. The feldspar is two thirds 

 microperthite, the remainder showing no sign of twinning or of 

 iutergrowths. There ie a bit of oligoclase, and there are some 

 small patches of quartz vermicuU. The microperthite often 

 ehows a further intergrowth of micropegmatitic aspect, the one 

 feldspar exhibiting no sign of the microperthite intergrowth, the 

 other showing it beautifully and the whole producing a striking 

 combination in thin section. It is clearly a growth of two feld- 

 spars, notwithstanding the resemblance to micropegmatite. J 

 mile beyond another ledge of syenite is found in the woods, 

 i mile northwest from the track, but it does not furnish fresh 

 material (902). Jt is however of the same type as the rock from 

 the cut. 



