122 NEW YORK STATE MUSEUM 



gneisses and rarely the quartzite. The limestones were too easily 

 soluble to leave any core of unmelted material. 



The Later Igneous Rocks 

 The Diabase Dikes 



After the solidification of the major igneous bodies treated above, 

 they were all subjected to mountain-making processes associated 

 with dynamic disturbances, stresses and rise in temperature. Under 

 these agencies profound changes were wrought, as has already been 

 suggested, greatly altering the rocks in character and mineral con- 

 tent, the older rocks being more altered than the later ones because 

 of their subjection to several periods of stress. 



Erosion still continuing, the area was reduced to a more or less 

 uniform plain. Along lines of weakness in the rocks, up through 

 cracks and joint planes the dying-out igneous activity played its 

 last role in the form of a lava oozing upwards and filling fissures 

 and rock openings and forming what are known as diabase dikes. 

 They consist of black, rocky bands cutting the older rocks indiscrim- 

 inately. This lava welled up from some deep-seated reservoir and 

 may or may not have reached the then surface of the land. Whether 

 the dikes were the supplying channels to extensive surface lava 

 flows or supported active volcanic action is an unsettled question, 

 for all surface rocks have been carried away by erosion. 



In the region here treated these dikes are rather uncommon, 

 only seven having been seen. One is splendidly shown on the south 

 shore of Lake Clear. It is 5 feet wide, runs east-northeast, and 

 can be seen either from the water or along the side of the state high- 

 way which runs to Saranac Inn. At one outcrop it was observed 

 that it was faulted a foot laterally, that is, a portion has been dis- 

 placed or side-stepped showing that since its solidification the area 

 has been further subjected to dynamic forces. It probably con- 

 tinues to the railroad cut 4 miles west of Saranac. 1 There are three 

 dikes in the anorthosite syenite contact zone in the road metal 

 quarry at Mountain pond. 2 They are respectively 3, 9 and 24 

 inches wide, and run very nearly east and west. They have been 

 more or less squeezed and faulted, for they perhaps lie along a fault 

 line. Another dike is situated in the town of Saranac Lake, cutting 



!H. P. Cushing, 18th Rep't of the N. Y. State Geol., Prem. Rep't on the 

 Geol. of Franklin Co., p. 122, dike 37. 



2 H. P. Cushing, 18th Rep't N. Y.'_State Geol.^dike 25. 



