84 EOCKS FORMED THROUGH IGNEOUS AGENCIES 



rise to a structure known as ophitic. (See Fig. 4.) The rocks are 

 compact, fine, and homogeneous, though sometimes porphyritic 

 and more rarely amygdaloidal. 



Colors. — The colors are sombre, varying from greenish 

 through dark gray to nearly black, the green color being due to 

 a disseminated chloritic or serpentinous product resulting from 

 the alteration of the augite or olivine. 



Classification. — Two principal varieties are recognized, the 

 distinction being based upon the presence or absence of the 

 mineral olivine. We thus have: (1) diabase proper and (2) oli- 

 vine diabase. 



Many varietal names have been given from time to time by 

 different authors. Gumbel gave the name of leucophyr to a 

 very chloritic, diabase-like rock consisting of pale green augite 

 and a saussurite-like plagioclase. The same authority gave 

 the name epidorite to an altered diabase rock occurring in small 

 dikes in the Fichtelgebirge, and in which the augite had become 

 changed to hornblende. He also designated by the term pro- 

 terobase a Silurian diabase consisting of a green or brown, 

 somewhat fibrous hornblende, reddish augite, two varieties of 

 plagioclase, chlorite, ilmenite, a little magnetite, and usually a 

 magnesian mica. The name ophite was used by Pallarson to 

 designate an augite plagioclase eruptive rock, rich in horn- 

 blende and epidote, occurring in the Pyrenees. The researches 

 of M. Levy Kuhn^ and others showed, however, that both horn- 

 blende and epidote are secondary, resulting from the augitie 

 alteration, and that the rock must be regarded as belonging to 

 the diabases. 



The Swedish geologist, Tornebohm, gave the name sahlite dia- 

 base to a class of diabasic rocks containing the pyroxene sahlite, 

 which occurred in the province of Smaaland, and in other 

 localities. The name teschenite was for many years applied to 

 a class of rocks occurring in Moravia, which, until the recent 

 researches of Eohrbach, were supposed to contain nepheline, but 

 which are now regarded as merely varietal forms of diabase. 

 Vanolite is a compact, often spherulitie, variety occurring in 

 some instances as marginal faeies of ordinary diabase. The 

 name eiikriie or eucrite was first used by G. Eose to designate 

 a rock consisting of white anorthite and grayish green augite 



^ Untersuchungen iiber pyrenaeisehe Ophite, Inaugural Dissertation TJni- 

 versitat, Leipzig, 1881. 



