1879. | Geology and Paleontology. 399 
GEOLOGY AND PALAONTOLOGY. 
Tue Tertiary Eruptive Rocks.—The trachytic formation is 
a most interesting one, but also very complicated. 
may be considered as the cradle of our notions respecting it since 
the time of Beudant. Richthofen imported the classification to 
California as it was established about eighteen years ago, based 
chiefly on habitus-characters. The geologists of the Vienna 
school have continued the study of it, and about some twelve 
years ago they published the geological map of Hungary too, 
also showing the considerable progress made since the departure 
of Richthofen. 
The geologists of the 4oth parallel have accepted as a base the 
classification of Richthofen, but with some alterations suggested 
by Zirkel; and that is about the classification adopted by Endlich 
and the other geologists of Prof. Hayden’s staff, with the only 
difference that they have abandoned the propylite. . 
Owing to the method employed, the petrographical part, as 
regards the feldspars, the true base of classification is incomplete: 
firstly, the plagioklastic feldspars are not distinguished specially; 
secondly, every glassy feldspar has been taken for (potash) sani- 
dine, which is not the case. 
In Hungary and some adjacent countries, the trachytes have 
been the object of my detailed studies nearly since Richthofen’s 
time. I commenced as field-geologist, and have continued as 
such, but making the aid of petrography serviceable to my field- 
_ work. I came to the conviction that those two branches of inves- 
tigation are contributing to the appreciation of the true nature of 
the eruptive rocks in a surprising manner; the mineralogical 
association also agreeing with the chronology of the eruptive 
rocks belonging to the same cyclus of eruption. Sa 
If you have no objection I will give a sketch of my classifica-. 
tion of the Tertiary eruptive rocks : 
I. Basalt, Leucitite. 
2. Augite—Anorthite, Trachyte (no quartz, no biotite). This in 
its normal state is the porphyre trachytique of Beudant, the 
andesite of Buch, the augite of German geologists; in its modi- 
fied state it can take up the habitus of greenstone (augite propy- 
lite), and in other circumstances it may become basaltic, but it is 
never rhyolitic. 
3- Biotite—Amphibole-Labradorite Trachyte. Without or with- 
quartz, without or with augite. 
n its normal state it may belong to the “echter trachyt” of 
the Austrian geologist, or to the amphibole-andesite. It can take 
up the greenstone (amphibole-propylite), or the basaltic, and very 
imperfectly the rhyolitic modification. 
In some Hungarian trachytes of this type the garnet occurs in 
oh the mineralogical association, apparently replacing the lime-feld- 
