CONTACT PHENOMENA. 223 



and many examples of the same in Sweden, which have been long known, 

 but lately brought again to mind by J. H. L. Yogt ; ^ all these are illus- 

 trations of the same process, and doubtless many nickeliferous pyrrho- 

 tites will fall in the same category. Whether any non-titaniferous iron 

 ores will be found which admit of this explanation remains to be seen. 



Contacts of Gabbro and Limestone.' 



The gabbro of the exposure north of Port Henry has been intruded 

 beneath and in part through crystalline limestone, into which it appears 

 to have also sent out some apophyses in the shape of dikes. Superb 

 contacts are shown in the railway cuts along the lake shore. The lime- 

 stone has been much disturbed by dynamic movements since the intru- 

 sion and exhibits strongly the characteristic plasticity of this rock under 

 such stresses. Next or near the gabbro it is coarsely crystalline and 

 abundantly charged with bunches, often of great size, of various silicates 

 peculiar to such situations. Dynamic movements have bent these into 

 many fantastic curves and shapes, often suggesting animals of various 

 sorts.t These bunches of silicates consist of quartz, plagioclase, diopside, 

 pale brown hornblende, scapolite, biotite or phlogopite, pyrrhotite, 

 tourmaline, titanite X and some other less common minerals. Rose 

 quartz is at times abundantly associated. These minerals often show 

 the effects of the dynamic movements mentioned above, and the writer 

 has already cited (in the reference given below) the case of a tourmaline 

 one and one half inches long which was bent around through an angle 

 of 70°. The minerals are in instances well bounded, especially when 

 calcite is particularly rich in the mixture, but in most cases they are 

 merely allotriomorphic aggregates, whose characters are best revealed 

 by the thin section. In the abandoned Pease quarry in the northerly 

 outskirts of Port Henry great horses of these silicates appear, and at the 

 top of the ledge formed by the quarry face is a large dike, doubtless an 

 offshoot of the underlying gabbro which one meets at the lake shore 

 below. It is itself somewhat metamorphosed. and shows allotriomorphic 

 brown hornblende, malacolite and plagioclase in all respects like those 

 described by the writer from the neighborhood of West Point on the 

 Hudson. § Contact masses of silicates similar to those above described 

 are characteristic of not a few exposures of white crj^stalline limestone 

 in this eastern part of the United States, and always near them the igne- 



* J. H. L. Yogt: Zeitschi-ift fur Praktische Geologie, vol i, 1893, pp. 4, 25, 257. 

 tThe be.st illustrations are on the north side of Split Rock, in the town of Essex, 

 t J. F. Kemp: Notes on the Minerals occurring near Port Henry, N. Y. Am Jour Sci., Juh%1890, 

 p. 62. 

 gj. F. Kemp: Dikes of the Hudson River Highlands. Am. Naturalist, August, 1888, p. G91. 



