PERIDOTITE DIKES NEAR ITHACA, N. Y. 265 



speaks of four dikes in a gorge near Ludlowville. This gorge is 

 the first one south of the road running east from the village. Two 

 of the dikes referred to by Vanuxem are located near an outcrop of 

 the Tully limestone; the other two are farther upstream, above a 

 high fall over the Genesee shale. The two dikes near the outcrop 

 of Tully limestone, together with a third located near the base of the 

 fall mentioned above, are each about an inch wide. 



Above the high fall, instead of two dikes there are four, all showing 

 on the south wall of the gorge. Three of these have been faulted; 

 the fourth does not reach up to the fault plane. The amount of the 

 displacement is about 2 feet. The largest dike is 7 inches wide 

 in its widest part; the others are all small, varying from 1 to 2 inches. 

 There is much branching, and it is doubtful whether more than one 

 of them reaches the top of the gorge wall. Farther upstream is 

 another fall. Above this fall are several small dikes. These are 

 all less than 2 inches wide and appear only on the south side of the 

 stream. 



In the gorge just south of the one above mentioned there are five 

 dikes, ranging from \ inch to 5 inches in width. These dikes may be 

 merely outcrops of some of those which appear in the other gorge ; 

 but unfortunately the intervening space is covered with glacial drift, 

 so that the continuity cannot be established. 



Just below Taghanic Falls, five small dikes, all less than 4 inches 

 wide, appear on the south wall of the gorge. At least one of them 

 reaches the top of the cliff. A thrust along a bedding plane has 

 displaced these dikes about 20 inches. There is much branching, 

 which often includes fragments of shale thicker than the dikes them- 

 selves. On the north wall of the gorge only three dikes were found. 

 Farther upstream, about 100 yards above where the wagon-road 

 crosses, there is a dike about 2 inches wide. 



In Glen wood Creek, above the railroad, a dike 7 J feet wide out- 

 crops in the bed of the stream. About 3 feet of the center of this 

 dike weathers like ordinary peridotite; the remainder takes on a 

 schistose appearance when weathered. This peculiar weathering 

 is due to the presence of many vertical cracks along which disin- 

 tegration progresses rapidly. 



Besides the dike in Six-Mile Creek which was mentioned by 



