246 The American Geologist. October, is95> 
cases, however, althougli the action of the atmosphere is so 
strikino^, the results are purely superficial, and a specimen of 
rock taken from within a few inches of the clay products seldom 
shows a trace of hydrous decomposition, even in thin sections 
under the microscope. This is just as true for such delicate 
minerals as olivine and nepheline as for the comnioner silicates. 
In many of the basic dykes, certainly i)re-Cretaceous and prob- 
ably Lower Palaeozoic in age, the absence of serpentine is so 
complete that unusual precautions are often necessary for the 
determination of the olivine, whilst in the numerous occur- 
rences of dunite throughout the Madras Presidency serpentine 
is extremely scarce." 
Mr. Holland would account for this wide difference in the 
conduct of the olivine in Indian and European localities on 
the supposition that the European areas had, during the later 
geological periods, been submerged below the sea, while in 
southern India there are no evidences of any such depression 
since Lower Palaeozoic time. 
Just what would be the effect of prolonged submergence 
in sea-water on a mass of olivine rock the writer is not pre- 
pared to say, but he does express the doubt if simple weather- 
ing of the mineral is ever productive of serpentine. Has there 
been ever advanced any proof that serpentinization is a super- 
ficial phenomenon? If due to weathering we ought some- 
where to meet with masses which are superficially converted 
intO' serpentine and gradually resume their normal character 
at greater depths. 
So far as is to be judged from available literature the 
olivine granules in any mass of rock, however dense, show no 
greater degree of hydration (serpentinization) near the surface 
or along contacts where surface waters would most readily per- 
meate, than in the interior of the mass. Further than this, 
serpentinization is as common, so far as the LTnited States is 
. concerned, in the arid portions of the West as in the humid 
East. In fact, this phenomenon is apparently entirely inde- 
pendent of climatic conditions. Is not the inference, then, fair 
that the process has gone on entirely independent of surface 
waters? 
Although convinced that excepting in the purely physical 
weathering of arid regions hydration is a most important fac- 
