1870.] HUNT — ON NORITE OR LABRADORITE ROCK. 31 



*' AsPiDiUM FiLix-FCEMiNA " — IS the Same species mixed with 

 Ci/st. bulb if era. 



'' WooDWARDiA virginica" — (p. 670) is the true plant from 

 New Jersey. 



" Woodwardia THELYPTERioiDES " — (p. 670) consists of a 

 smallish frond of W. Virginica, and one of Aspidium Thdypteris. 



ON NORITE OR LABRADORITE ROCK. 



By T. Sterry Hunt, LL.D., F.R.S. 



[Read before the American Association for the Advancement of Science, at 



Salem, August, 1869.] 



{From Silliman's Journal for March, 1870.) 



The various rocks composed essentially of a triclinic or anorthic 

 feldspar, with an admixture of hornblende, pyroxene, hypersthene 

 or diallage, have by lithologists been designated by the names of 

 diorite, dolerite diabase, hypersthenite and gybbro, among others. 

 The latter name has by many been regarded as synonymous with 

 euphotide. I, however, pointed out many years since that the true 

 euphotide is not a feldspathic rock, but consists of a mixture of 

 diallage with saussurite, a white heavy silicate apparently identical 

 with zoisite. By an admixture of labradorite or an allied feldspar, 

 however, euphotide passes into the so-called gabbro, which I have 

 defined as a diallagic diabase, and which is closely related to norite. 

 The name of hypersthene rock or hypersthenite (sometimes con- 

 tracted into hyperite), was given by MacCulloch* to a rock 

 consisting of labradorite, or a related feldspar, and hypersthene, 

 found by him in the Western Islands of Scotland, and subsequently 

 recognized by Emmons in the Adirondack Mountains of Northern 

 New York. By both of these observers it was regarded as an 

 erupted rock. In 1851, I detected it among the Laurentide hills 

 of Canada, where, as in New York, it extends over considerable 

 areas. Farther examinations of this rock in place showed that 

 though hypersthene, generally in very small proportion, is a 

 frequent element, it is often replaced by a green granular pyroxene, 

 and still more often both of these are wanting, so that we have a 



^ MacCulloch, Geology of the Western Islands, i. 385-390. 



