1894.] Geology and Paleontology. ` 413 
al. It is not known that the dikes are younger than the sedimentary, 
for they were nowhere found in contact. The strata of the basin are 
now seen at the same level with the dikes, but faulting and a synclinal 
fold have clearly lowered them with reference to the granite on either 
side. Finally, it is probable that the dikes are not limited to the 
vicinity of the sedimentary basin. Neither end of the belt containing 
the dikes was determined, and an observation by Professor G. H. Stone 
shows plainly that sandstone dikes do occur in the same general strike 
line far removed from any sedimentary rocks. (Bull. Geol. Soc. Am. 
Vol. 5, 1894.) 
The Origin of the Vichy Mineral Waters.—M. Dollfus has 
been making a study of the geology of the environs of Vichy and comes 
to the following conclusions as to the origin of the celebrated medicinal 
water of that region. 
The waters charged with soda derived from the decomposition of 
porphyry percolate the earth in contact with carboniferous conglomer- 
ates and the Culm strata flowing in a synclinal. When their down- 
ward course is checked by the granules or the micropegmatites which 
are impermeable, they reascend through the tertiary beds. Here their 
flow is partially impeded by the arkose beds which are topped by the 
Cusset Marls, and an immense water sheet is formed near the contact 
of these two formations. Atmospheric waters are here the important 
factors, and the carbonic acid gas with which they are charged becomes 
an active agent, displacing even the silicic acid of some of the felds- 
pathic compounds. In short the alteration is set up at the surface ; 
decomposition and kaolinization of the porphyrites goes on, under our 
eyes, at the surface, for, below we see compact, unaltered rocks, in 
which no chemical activity is apparent. ; 
The origin of the carbonic acid is more difficult to explain. Since 
the atmospheric waters do not furnish a large enough supply, some of 
it, as well as the lime, must be derived from chalks of Vernet and the 
water-bearing marls of Cusset. The phorphyritic strata are limited 
around the Central Plateau; the presence of granite, sd vis oar of im- 
Pervious clay, an abundance of lime, and all the peculiar series of con- 
ditions which are met with at Vichy and no where else, explain the 
formation of these peculiar mineral waters and their isolation in the 
midst of hydraulic basins of which the products are so very different. 
(Rev. Sci. Mars, 1894.) 
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