Ay) RICHTHOFEN—NATURAL SYSTEM 
that this activity has continued with extreme violence over all parts of the globe, 
through the remaining part of the Tertiary and the Post-tertiary periods, growing, 
however, more and more faint during the latter. Propylite was, in fact, the precursor 
of all other volcanic rocks, and its appearance on the surface inaugurated a grand 
revolutionary activity on the globe. It is this position, at the entrance as it were to a 
new era in the history of the earth, which has given rise to the name ‘‘ propylite.” 
Mode of Geological Occurrence.—The position of propylite at the bottom of all 
voleanic rocks is its most important geological feature. Its age has in no instance been 
ascertained with exactness. The nearest approach to its determination was made in 
Northern Transylvania, where I found, in several localities, nummulitic strata inter- 
sected by dykes and large intrusive masses of propylite, and covered by accumulations 
of it. As the greater part of the volcanic rocks in that country are of Miocene age, 
the ejection of propylite must have taken place either in the latter part of the Hocene 
or in the earlier part of the Miocene epoch. In view of the facts, that volcanic rocks 
have nowhere been observed to be anterior to the Hocene (probably even not prior to 
the Miocene) epoch, and that propylite is always allied to them as the first link in the 
order of succession, it may be inferred that propylite is, in general, of Tertiary age, 
until proofs to the contrary may be found. 
The forms of propylitic mountains can be observed only in rare instances, since 
they are usually covered by other volcanic rocks, especially by andesite. This cireum- 
stance may also explain the fact of the comparatively rare occurrence of propylite as a 
surface-rock. In the environs of Bisztritz, in Northern Transylvania, it forms several 
high, isolated cones with steep slopes, resting on Eocene strata; their fine, dome- 
shaped appearance is scarcely surpassed in beauty by that of any other kind of rock. 
No estimate can be made in regard to the relative bulk of propylite which has been 
ejected, on account of its being overlaid by andesite and trachyte. It occurs, as far 
as exposed to view, in quite considerable accumulations, at Nagybanya and Kapnik, 
in Hungary, in Washoe, and at Silver Mountain, and covers large areas in Mexico, 
where it overlies the Cretaceous. It appears to have been profusely ejected through 
fissures, and its emission not to have been accompanied by volcanic action proper ; no 
distinct traces, at least, have been found of propylitic voleanoes. Massive eruptions 
‘are known to have occurred, besides the places mentioned, in several other parts of 
the southern slope of the Carpathians, on the highlands of Armenia, and in Mexico, 
while the occurrence of propylite in Bolivia, the Altai Mountains, Northern China, 
and some other countries, may be inferred from the description of their geology. 
Propylite has been repeatedly considered to be a sedimentary rock, metamor- 
phosed iz situ. The cause of this opinion was probably the fact that there are rocks 
which undoubtedly have had that mode of origin, and share with propylite the resem- 
blance in mineral character to diorite. The eruptive origin of propylite is, however, 
evident, as it intersects stratified rocks in the shape of dykes. In Washoe and Silver 
Mountain, moreover, there are extensive accumulations of propylitic breecia and 
stratified tufa. The latter consists of alternate layers of coarse conglomerate, fine- 
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