ee RICHTHOFEN — THE NATURAL SYSTEM 
Orper Tuirp: Propylite. _ 
Family 1. Quartzose propylite. 
“2. Hornblendie propylite. 
3. Augitic propylite. 
ce 
OrpvEerR FourtH: Andesite. 
Family 1. Hornblendic andesite. 
“2. Augitie andesite. 
Orpver Firtu: Basalt. 
Family 1. Dolerite. 
ee Basalt 
“3. Leucttophyre. 
Orper First—RuyYOLITE. 
‘ 
The name “rhyolite” was proposed, early in 1860, for certain rocks fre- 
quently occurring on the southern-slope of the Carpathians, and distinguished, in min- 
eral character, from trachyte, which they otherwise resemble, by the presence of quartz 
as an essential ingredient, and an almost infinite variety of texture. Beudant* had, 
long before, described certain varieties of these rocks as porphyre trachytique, pumice- 
stone, pearlite, ete. In 1861, the name “‘liparite” was proposed by J. Roth® for rocks 
of similar nature occurring on the Lipari Islands. The term ‘‘ rhyolite,” however, 
being of prior date, has since been almost generally adopted, among others by F. v- 
Hochstetter, for rocks from New Zealand, by C. Peters, G. Stache, and others for those 
of Hungary and Transylvania, by Ferd. Zirkel for those of Iceland, by B. v. Cotta as 
a general term in his ‘‘ Gesteinslehre.” The word ‘‘rhyolite” is designed to express 
one of the prominent features of these rocks. It is this: that their chief varieties 
have the appearance, as it were, of natural glasses, and bear evidence, more than any 
other rocks do, to the unpracticed eye, of having been flowing in a viscous state. 
Mode of Geological Occurrence —Rhy olite has had its distinct epoch of eruption in 
relation to other volcanic rocks. Wherever it occurs it may be easily proved to have 
been of more recent origin than either propylite, andesite, or trachyte, but to have 
preceded basalt in age. As to its geographical distribution, it is confined to the im- 
mediate neighborhood of one or all of those antecedent rocks, and oceurs ordinarily 
within their very limits. Until lately, not much attention had been paid to it. But 
since the establishment of the name, rhyolite has been found to be widely distributed, 
though always occupying a subordinate position. In Hungary it usually skirts the 
lower part of the flanks of andesitic ranges, forming hillocks and ridges of little 
elevation, fillmg depressions, and issuing in currents from fractures, and, in general, 
giving evidence of its entire dependency on the places of previous eruptions. 
The greater portion of the rhyolite has, in that country, been evidently ejected 
by volcanic activity. It appears that the same may be said in regard to the 
3 Loe. Cit. 4 Voyage en Hongrie. Paris, 1820. 5 J. Roth, die Gesteins-analysen. Berlin, 1861. 
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