SCIENTIFIC SUMMARY. 
431 
The presence of these readily alterable basic glasses at once reveals the 
source of the clayey matter with which they are associated, as wherever 
rocks of this type occur, their decomposition into clay is observable. 
Among the minerals present in the volcanic ash are rhombic tabular 
crystals of plagioclase, augite, magnetite, and a little sanidine or hornblende. 
It is singular that quartz-grains are practically absent, in striking contrast 
to coast deposits. This fact, however, is not so unexpected as the formation 
of zeolites in the free state. Minute fibrous radiated spherules are formed in 
the mud, possessing the crystallographic characters of christianite. Besides 
these zeolitic spherules, other crystals of the same kind occur in the form of 
minute prisms, and in such prodigious numbers that they make up about 
one third of the red clay. These and the zeolitic spherules are regarded 
by tlie authors as belonging to one mineral species, and they remark that 
the formation of these, and of the red clay in which they are developed, is 
easily understood if we bear in mind the lithological nature of the basic 
tuffs, and of their products of decomposition. — {Nature, September 18, 1879.) 
Mud- Volcanoes . — Professor Giimbel of Munich has communicated to the 
Bavarian Academy {Sitzungber. 1879), a paper on mud-volcanoes and their 
products, his examination of which leads him to the following results. The 
mass of mud erupted is nothing but softened argillaceous, or sandy-argil- 
laceous, stratified rock, derived from the immediate vicinity, and probably 
brought up from no great depth. It often contains organic remains, whilst 
true volcanic products (such as ashes, lapilli, lava, and pumice), take no part 
in its formation. It is only exceptional, if in the midst of volcanic for- 
mations the latter, softened superficially like the stratified rocks by gas and 
water, furnish the eruptive material, and indeed no such case is yet known 
with certainty. 
Besides the abundant outflow of water, the efflux of gases at high pressure 
is necessarily and genetically connected with mud-volcanoes. Among these, 
carburetted hydrogen holds the first place. The high tension of the gases 
which flow out, and the long duration of the phenomena, do not infer the 
existence of a great accumulation low down in the earth, because upon such 
a supposition the provision must be exhausted in a comparatively short time. 
The persistent formation especially of the carburetted hydrogen, the principal 
of these eruptive gases, necessarily presupposes the presence of organic 
constituents in the deeper seated stratified rocks, and this is also confirmed 
by the regular occurrence of petroleum, naphtha, asphalte, or bituminous 
materials in connection with mud-volcanoes. It is not improbable that 
phosphuretted hydrogen is also produced during this process of decomposi- 
tion, and the presence of this gas would furnish a satisfactory explanation of 
the frequent spontaneous ignition of the outflowing gases. On the other hand, 
the more abundant occurrence of carbonic acid would seem to indicate a 
certain approach to volcanic processes. 
The intermixture of soluble salts, especially chloride of sodium, in the 
mass of mud, may be explained in part by the circumstance that many 
mud-volcanoes are situated in the vicinity of the sea, or upon a soil soaked 
with sea water. In favour of this, we have the presence of iodine and 
bromine in the mass of salts produced. It may also be assumed that the 
strata contiguous to the channel of eruption may contain abundantly such 
