A PERIDOTITE DIKE IN PENNSYLVANIA COAL MEASURES 5 II 



The second record by Vanuxem is that of a dike near Manheim 

 Bridge, on East Canada creek, 75 or 80 miles east of Syracuse. 

 The dike comes up on a well-known fault between the Beek- 

 mantown limestone on one side and the Trenton and Utica 

 formations on the other. (See p. 270 of Vanuxem's Report.) 

 The petrography of this and of more recently discovered neighbor- 

 ing dikes has been worked out by C. H. Smyth, Jr., who proves 

 that the rock is the rare and interesting species alnoite, a 

 melilite-basalt. The dike strikes with the fault, which varies 

 from N. 40 E. to N. 20 E., the former bearing being the 

 direction where the dikes are exposed. P. F. Schneider sub- 

 sequently identified five dikes, all of which cross the creek. 1 

 This rock is of much interest in connection with the new occur- 

 rence here described, even though no melilite has been as yet 

 demonstrable in the latter. Professor Smyth has also worked 

 out some extremely interesting data regarding the amount of 

 weathering since the disappearance of the glacial ice-sheet. 



The third occurrence mentioned by Vanuxem is of four narrow 

 dikes near Ludlowville, N. Y., in the Genesee slate (p. 169 of 

 his Report). Ludlowville is about ten miles north of Ithaca 

 on the east side of Cayuga lake, and is approximately fifty miles 

 southwest of Syracuse. As will appear, the region about the 

 southern end of Cayuga lake is another center of fairly numerous 

 outbreaks. The original discovery has since been added to by 

 others in and near Ithaca, and in the largest case of all, in a 

 small ravine, a mile south of Glenwood, a dike, has been reported 

 by V. H. Barnett which is certainly 25 ft. and may be more 

 than 100 ft. in width. These dikes cut the Devonian strata as 

 high up as the Portage. The petrography has been most care- 

 fully worked out by G. C. Matson. Olivine and biotite are the 

 chief minerals present, with less abundant diopside, magnetite, 



'C. H. Smyth, Jr., "A Third Occurrence of Peridotite in Central New 

 York," Amer. Jour. Sci., April 1892, p. 322. "Alnoite Containing an 

 Uncommon Variety of Melilite," Idem, August 1893, p. 104." Weathering 

 of Alnoite at Manheim, N. Y.," Bull. Geol. Soc. Amer., IX., 1897, p. 257. 

 P. F. Schneider, "The Correlation of Some Alnoite Dikes in East Canada 

 Creek, N. Y.," Science, Nov. 24, 1895, p. 673. The first dike discovered is 

 illustrated in the cut on p. 247 of Scott's Introduction to Geology. 



