14 Report of the State Geologist. 



effect produced in New York was much less pronounced and mainly effective 

 in the production of faults, the rocks being only slightly folded and not 

 metamorphosed at all. The faults, however, are very numerous and often of 

 considerable magnitude. The present topography is largely due to their 

 presence and they have no doubt frequently served as lines of readjustment 

 since they were originally formed. 



X. Post - Uiica Pikes. During or subsequent to the time of the 



dynamic movements just referred to, igneous rocks made their way toward the 



surface through fissures. They are now found mainly as dikes and, as 



shown by Kemp, are of two widely different types, both very basic rocks 



(camptonites, monchiquites, fourchites) and quite acid rocks (trachytes) 



occurring. The basicity of the one type and the acidity of the other seem 



somewhat more pronounced than in the case of the supposed Pre-cambrian 



basic and acid dikes. As far as New York state is concerned, these dikes 



seem confined to the vicinity of lake Champlain, not ranging westward as do 



the earlier dikes. 



Faults. 



The true boundary, if its minutiae could be mapped on a large scale, 

 would necessarily be exceedingly irregular. The Potsdam was laid down on 

 an uneven floor, especially so when the Grenville series formed that floor, and 

 where it has been pared away by erosion down to its very base this irregu- 

 larity of floor must make a highly tortuous contact line. These minor details 

 are for the most part obscured by the drift covering. An interesting illustra- 

 tion is furnished by exposures two miles south of Nicholville, St. Lawrence 

 county, which will be described in their appropriate place.* 



While some of the contacts are clearly those of deposition others are 

 unquestionably due to faulting. The much-faulted structure of the eastern 

 Adirondacks has been emphasized in previous reports by Professor Kemp and the 

 writer. In the district under consideration here, the evidence is less pro- 

 nounced, but that faults are present, and that numerously, is clear. The well 

 known outcrops of Potsdam sandstone along the Racquette river south of 

 Potsdam lie along the west side of a fault. The outlier of gneiss at Burke 

 village, Franklin county, seems brought up by a pair of faults. Two miles 

 northeast of Whippleville, Malone township, are Potsdam exposures whose 

 attitude is due to faulting. 



*The areal results of the work are delineated, so far as may be, on the accompanying map. As outcrops of the 

 Potsdam sandstone are very infrequent much of the boundary as there shown can only be regarded as a reasonable 

 approximation, it being marked at the limits reached by the Pre-cambrian outcrops, with such aid as the topography 

 furnishes. Westward from Parishrille its true position is quite uncertain, the conditions being much more complicated 

 than those prevailing to the eastward. 



