PERIDOTITE DIKES NEAR ITHACA, N. Y. 275 



limb of this same anticline there has been a movement along a bedding 

 plane. This movement has faulted four dikes on the south wall of 

 Taghanic Gorge and three dikes in a gorge east of Ludlowville. 

 The amount of displacement of the ends of the dikes is only about 2 

 feet, and the movement is largely confined to a single bedding plane. 

 The dikes are nearly at right angles to the axis of the fold, and hence 

 eighteen inches can hardly be taken as the measure of the amount 

 of movement. Probably the movement was nearly parallel to the 

 dikes, and, if so, the amount of actual displacement might be several 

 times the distance between the severed parts of the dikes. Slicken- 

 sides are not noticeable, but the bedding plane is occupied by a thin 

 layer of pulverized shale. At first the possibility of the dikes having 

 passed for a short distance along this bedding plane was considered. 

 This theory was discarded, because all the dikes showed the same 

 displacement; and the clay between the strata did not contain any 

 of the mica scales which are so prominent in the clays derived from 

 the disintegration of the dikes. 



The sequence of the earth movements in this region appears to 

 have been as follows: folding with the development of joint planes; 

 the intrusion of the dikes and their consolidation; renewed folding, 

 accompanied by minor thrust-faulting and movements along bedding 

 planes. The relation of the folds of this region to those of the Appa- 

 lachian Mountains makes it clear that the periods of folding must 

 have been the same. It follows, then, that the dikes are probably 

 younger than the earliest period of folding and older than the latest. 

 This would fix the date of the intrusion near the close of the Paleozoic. 



