96 THE CRYSTAL FALLS IRON-BEARING DISTRICT. 



United States, have advocated the simpHficatiou of petrographical nomen- 

 clature, I used the term basalt, now ordinarily used for the Tertiary or post- 

 Tertiary basic rocks. This term was, however, modified by the prefix 

 "apo," as indicating their altered condition and the presumed presence of a 

 glassy base.-' This was a logical continuation of the use of the prefix as 

 proposed by Dr. Bascom^ for devitrified acid lavas. 



More detailed studies upon the Hemlock volcanics have shown the 

 presence of rocks which were apparently originally holocrystalline, and 

 therefore do not belong with the altered vitreous basalts, the apobasalts, and 

 others in which some of the glass is apparently unaltered. Consequently, 

 since the apobasalts comprise only a portion of the Hemlock volcanics, the 

 replacement of that term as a general heading by the older, more general, 

 one of basalt was considered. 



The use of this term is, however, not altogether satisfactory, for the 

 rocks, while clearly recognizable as basalt derivatives, do not possess the 

 mineralogical composition of the basalts. The term "apo" having been 

 restricted, as above indicated, can not be applied to them, for their altera- 

 tion is in many cases metasomatic and dynamic, and in most cases not 

 devitrification. If we adopt the prefix "meta" to indicate alteration of all 

 kinds, then these rocks could be called " metabasalts." 



The terms "metadolerite," "metadiabase," etc., were proposed by Dana^ 

 for metamorphic dolerites, diabases, etc., and first used by Hawes* in the 

 description of the altered rocks around New Haven. Recently these terms 

 have been revived, but with a very different significance from that with 

 which they were first used. It is proposed to designate by such terms 

 "rocks now similar in mineralogical composition and structure to certain 

 igneous rocks, but derived by metamorphism from something else."^ Fol- 

 lowing this suggestion, an uralitized dolerite (diabase) would be called a 

 metadiorite. Such a use of the term does not seem justified, and the 



' Loc. cit., p. 805. 



"The structures, origin, and nomeuolature of the acid volcanic rocks of South Mountain, by 

 Florence Bascom. Jour. Geol., Vol. 1, 1893, p. 828. 



' Chloritic formation of New Haven, Connecticnt, Ijy J. D. Dana : Am. Jour. Sci., 3d ser., Vol. XI, 

 1876, pp. 119-122. 



■•The rocks of the "chloritic formation" on the ■western border of the New Haven region, byG. W. 

 Hawes : Am. Jour. Sci., 3d ser., Vol. XI, 1876, pp. 122-126. 



■'"On a series of peculiar schists near Salida, Colorado, by Whitman Cross: Proc. Colo. Sci. Soc, 

 ip. 6, footnote. Paper read Jau. 2, 1893. 



