OF VOLCANIC ROCKS. 7) \ 
the ‘‘transition rocks.” Since then, the names greenstone, greenstone-porphyry, 
diorite, dioritic porphyry, and others, have frequently been applied for the same rocks 
of the Carpathians. Similar names have been used for them when they were mentioned 
as occurring in other countries, as for instance Mexico, where still oftener they have 
been simply styled ‘‘ porphyry.” In 1860, having had sufficient evidence of the Ter- 
tiary age of these rocks and their close connection with the voleanic rocks of that 
period, I separated them, in a treatise on some voleanic countries in Hungary, already 
referred to, by the name of ‘‘ greenstone-trachyte,” from the remainder of those rocks 
which then were usually comprehended by the name trachyte. That designation has 
since that time been frequently applied in geological descriptions. The attempts made 
to classify the rocks included in it have, however, been rather unsuccessful. J. Roth 
combines them into one group with amphibol-andesite, from which they are quite dis- 
tinct as regards their petrographical as well as their geological properties ; while others 
considered them as belonging to the dioritic rocks. The grounds upon which they 
have been united with the latter are purely artificial, since diorite is, from a geological 
greenstone-trachyte.” Breithaupt established 
ue 
point of view, widely separated from 
a new name, ‘‘Timacite,” for a variety of our propylite, which is of very limited oceur- 
rence, and in which he discovered a new variety of hornblende, called by him ‘“ gamsi- 
gradite.” Most valuable contributions for the knowledge of our “ propylite,” were 
recently given by Dr. Guido Stache, from observations made in Transylvania. (Hauer 
and Stache, Geologie Siebenbiirgens, Vienna, 1865.) He discovered the occurrence, 
in that country, of quartz-bearing varieties in greater extent than they have been 
found hitherto at any other place. Stache retains the name ‘ greenstone-trachyte,” 
for those varieties which contain no quartz, and proposes the name “ Dacite” (from 
the Roman province of Dacia to which Transylvania belonged) for those of which 
quartz is a common ingredient. 
These statements will show the discrepancy of the views which have been 
entertained in regard to the systematic place and the nomenclature of the rocks 
under consideration. It is owing, partly to their twofold affinity with other rocks, 
(mineralogically to diorite, and geologically to voleanic rocks) and partly to the fact 
that they had, until lately, not been made the object of study. All observations made 
during the last few years concur in this, that those rocks, wherever they have been 
encountered, form a distinct link in the range of Tertiary and Post-tertiary eruptive 
rocks, being everywhere the first of them in age, while they are, in regard to their 
mineral character, no less distinct from any other eruptive rocks originated in those 
periods. They constitute, indeed, a more natural and more distinct group than any 
of the other volcanic rocks, and it has become desirable to unite them under a com- 
mon designation. As no prominent property distinguishes them from diorite, and the 
derivation of the name from one certain locality did not appear proper for the desig- 
nation of rocks of wide distribution, geological relations alone could be used as a basis for 
the nomenclature. The rocks under consideration, as we shall hereafter more fully 
develop, give evidence, in all localities where they have been met with of having re- 
opened the eruptive activity after ages of comparative repose. It is since then only, 
WW (59) 
