OF VOLCANIC ROCKS. 2t 



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 volcanic rocks of that 

 period, I separated them, in a treatise on some volcanic 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 

 point of view, widely separated from "greenstone-trachyte." Breithaupt established 

 a new name, " Timacite," for a variety of our propylite, which is of very limited occur- 

 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, Geologic Siebenbiirgens, Vienna, 1863.) 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 volcanic 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, 



ii (.59) 



