GEOLOGY OF LAKE PLEASANT QUADRANGLE 



31 



In the bed of West Sacandaga river just above The Gorge, 

 a dike, 4 feet wide and traceable 50 feet, Hes in the ten-foot wide 

 crushed zone of a fault. It is all coarsely brecciated except a 

 narrow tongue which extends 10 feet into the country rock. While 

 we can not be positive that this molten rock was intruded along a 

 fault, we are at least certain that movement along a fault here 

 took place after the intrusion. This is the only one of the dike 

 rocks (no. 41 of table) w4iich fails to have a porphyritic texture. 



Two small dikes (nos. 40 and 46 of table) from 10 to 25 feet 

 wide and 50 to 60 feet long occur along a fault in the bed of Nine- 

 mile creek. In the more southerly one (no. 40 of table) the rock 

 is much broken as a result of fault movement. The more northern 

 one shows contact with pink granite. Both dikes have porphyritic 

 and diabasic textures. 



On the road, one-half of a mile below the mouth of West Branch 

 Sacandaga river, a very small portion only of a diabase dike may 

 be seen in contact with a syenite-looking rock. This rock is differ- 

 ent from the others in lacking a diabasic texture and containing 

 considerable hypersthene (no. 43 of table). 



The largest dike, 300 feet long and 30 feet wide, is located about 

 a mile east of Benson P. O. Its north 70° west strike is exceptional 

 though it does lie parallel to the foliation of the country rock 

 which here is closely involved Grenville and igneous gneisses. 

 Toward the borders the dike becomes very fine grained while 

 throughout the mass phenocrysts only sporadically occur (no. 39 

 of table). 



Examples of gabbro and diabase 







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