1879. | Geology and Paleontology. 401 
orth, trachyte occurs in its normal porphyritic, syenitic or granitic 
state. 
On the map the greenstone-trachyte (propylite) and the rhyo- 
lite, as important habitus-characters, are to be signalized by a 
secondary mark on the respective trachytes. 
The chronological order has been established by means of the 
sedimentary formations formed wholly or partly by trachytic 
ejections, aided by the breaking of younger trachytic masses 
through older ones, in which case in the region of contact the 
minerals of two different types may be found mingled. 
The trachytic types as enumerated according to their order of 
basicity, exhibit at the same time also the chronological series of 
the eruptions. The limits of time for the trachytic formation in 
Hungary are the following: 
1. The eruption of the augite-anorthite trachyte took place in the 
Upper Miocene (Sarmatische Stufe). 
2. The biotite-amphibole labradorite trachyte corresponds to the 
Middle Miocene (Mediterranean Stufe). 
3. The biotite-andesite (oligoclase) trachyte appeared during the 
Lower Miocene. 
4. The biotite orthoclase trachyte is the product of the beginning 
of the trachytic cyclus'of eruption during the Upper Eocene. 
For the field-geologist, who visits a country for the first time, 
such a detailed classification is of course impossible; he must be. 
contented with a general one, but one which should still be in ac- 
cordance with the former. He may arrive at that by means of 
some microscopical minerals, some habitus properties, aided in 
Many cases even by panoramic characters of the single trachytic 
types, all that being taken into consideration not only on the 
eruptive rocks themselves, but also on the sediments containing 
trachytic fragments. 7 
o classes are easily distinguished: the augite-trachyte and 
the biotite-amphibole trachyte ; the former is the younger, the lat- 
ter the older. Since the time of Beudant, the “trachyte micassé 
rhyolite, while in other instances it breaks through it. On the 
line of contact the highest degree of rhyolithism is perceptible, 
while with the increasing distance the normal state is more and 
more preserved. 
The general features of these three classes are so prominent, 
that once acquainted with them, they are to be discovered every- 
