210 Barnett — Discovery of a New Dike at Ithaca, N Y. 



Art. XV. — Notice of the Discovery of a New Dike at 

 Ithaca, N T. ;* by V. H. Barnett. 



The occurrence of several dikes of igneous rock cutting the 

 Devonian shales and sandstones near Ithaca, N. Y., was recog- 

 nized as early as 1842. Yanuxemf records in his report on 

 the 3d District, the presence of four small dikes near Ludlow- 

 ville. Other small dikes, which were discovered by students 

 and professors of Cornell University, were described in a 

 paper by Prof. Kemp, J in 1891. This paper is the latest 

 published statement, so far as the writer knows, concerning 

 the dikes at Ithaca. According to Prof. Kemp, four dikes 

 were then known in the vicinity of Ithaca in addition to those 

 recorded by Yanuxem. Kemp was able to relocate but two 

 of Yanuxem's dikes, so that the total number then known was six* 



During the past season the writer, engaged as a field assistant 

 on the IT. S. Geological Survey, discovered in connection with 

 Dr. E. M. Kindle a number of hitherto unknown dikes in the 

 vicinity of Ithaca. Most of these dikes, like those previously 

 known at Ithaca, are thin sheets of peridotite generally from 

 one to five inches in width. The total number of dikes now 

 known to the writer near Ithaca exceed twenty-five. 



One of the newly discovered dikes is of such unusual size 

 for this region as to justify a brief preliminary notice. It is 

 exposed in a small ravine on the west side of Lake Cayuga 

 about one mile south of Glenwood. The dike is of light 

 greenish gray color with numerous inclusions of shale and 

 small limestone fragments. " The latter are probably derived 

 from the Tully limestone, which is some 450 feet below the 

 outcrop. The numerous included fragments give the mass a 

 breccia-like appearance. The direction is nearly north and 

 south, but the contact is irregular and clearly shown on the east 

 side, where the shale is considerably baked. On the west side 

 the dike passes under a mass of drift so that the total width is not 

 known. It is, however, not less than 25 feet thick. Another 

 dike mass, 13 feet in width, lies 150 feet to the west of the 

 one just described and is identical with it in appearance. The 

 latter terminates abruptly on the west along a joint plane of 

 the shale, and passes under the drift on the east. The relations 

 of the two masses suggest that they may represent a single 

 dike considerably more than 100 feet in width which pinches 

 out both north and south. In Indian Creek, about three- 

 quarters mile south of this outcrop, is a two foot dike and in 

 Glenwood Creek, to the north, a dike eight feet wide occurs. 



Ithaca, N. Y., January 24. 



* Published by permission of the Director of the U. S. Geological Survey, 

 f Rep. 3d Dist. N. Y. State Geological Survey, p. 169. 

 X This Journal (3), vol. xlii, pp. 410-412, 1891. 



