Rock- WcatJicring and Serpentiiiization . — Merrill. 247 
tor,* the absence of any but a very narrow zone of hydration 
products between the residual clay and fresh rock is not at 
all strange. Much depends on the texture of the rock and its 
mineral composition. In cases where the weathering is largely 
in the nature of solution and oxidization such abrupt changes 
are to be expected. The Fourche Mt. syenite, of Arkansas, 
an almost purely feldspathic rock, passes within the space of 
2 cm. from a line red-brown unctions clay to a massive fresh 
unchanged feldspar: the nepheline of the nepheline syenite of 
Mias in the Urals is eaten out below the surface of the more 
refractory feldspar, mica, zircons, etc., but gives in the closed 
tubes only traces of water and shows under the microscope 
only incipient stages of hydration. 
Aly own view of the case is, that the two phenomena are 
due to widely different causes; that serpentinization is a deep- 
seated process due to waters or vapours coming from consid- 
erable depths, and it may be even constituents of the magmas 
at the time of their intrusion. The almost complete absence 
of oxidization products in fresh serpentine is indicative of this. 
Again, serpentinization is a process involving a greater degree 
of hydration than is weathering. The serpentinized olivine 
rock of the Nijni Tagilsk platinum district yields 14.21 per 
cent, of water, while the brown crust which results from its 
weathering yields but 11.74 per cent. The serpentine of Har- 
ford county, Maryland, further, shows a loss on ignition of 
18.15 per cent.jf while the hard red-brown crust produced on 
the immediate surface, through weathering, loses but 11.82 
per cent., and the residual soil but 7.89 per cent. In the same 
manner soils derived by weathering from other highly hy- 
drate magnesian rocks, as the so-called soap-stone (altered 
pyroxenites), show a very considerable loss of water, even 
though the actual loss on ignition in the resultant soil may be 
a trifle greater than in the fresh rock. 
These facts are mentioned in detail here since they do not 
seem to have been before noted, or at least their significance 
not realized. If serpentinization were a product of weathering, 
a shorter exposure to atmospheric influences, as in India, 
*"R()cks and Rock-weathering," pp. 188, 234, etc, 
tin part due to C O, though the amount of this constituent cannot be 
over 3 or 4 per cent. 
