Rock-Weathering and Serpe?itifiizatto?i. — Merrill. 249 
changes his views or mode of expressing them as to call the 
deep-seated process Complicirte Verwitterimg, in distinction 
from the purely superficial Verwitterung, due to atmospheric 
action. Moreover, in the paper "Ueber den Serpentin," to 
which reference is made above, he describes the processes and 
results incidental to the Verwitterung of the serpentine quite 
independently of those incidental to its first production. 
Teall* apparently accepts unhesitatingly ideas contrary to 
those expressed by myself, for he says: "The alteration of 
olivine by surface agencies — water, carbonic acid, and oxygen 
— gives rise to serpentinous and other pseudomorphs." 
Consideration along these lines led the present writer in the 
work to which reference has been made to attempt making a 
distinction between true weathering and the more deep-seated 
process which he called hydrometamorphism. Surely pro- 
cesses so widely different as those resulting in the production 
of a serpentine from a peridotite and the final destruction 
through oxidation, carbonization, and partial dehydration of 
this same serpentine, should not be confounded under the same 
name. The distinction, it is true, is not one that can at all 
times be readily made. As the petrologist finds difificulty in 
separating his plutonic from the effusive rocks, so here are no 
hard and fast lines, and it is often impossible to state at just 
what point one shall assume that superficial processes cease 
and the deep-seated begin. The writer's conclusions are to the 
effect that the zone of oxidation forms the natural and easiest 
recognizable limit. The processes within this zone are those 
of weathering; those below, whether brought about by super- 
ficial waters deprived of their free oxygen and carbonic acid, 
or by deep-seated waters welling upwards, are those of hydro- 
metamorphism, metasomatosis, alteration, or whatever suitable 
name may be adopted. 
In conclusion, one might urge the necessity of closer ob- 
servations regarding the formation of serpentine from olivine 
or other anhydrous magnesian silicates. That it is through a 
process of hydration is self-evident, but as to the conditions 
under which it goes on literature is strangely silent. Is the 
process still going on in the exposed masses now open to our 
inspection, or is it at a standstill? The writer is of the present 
♦"British Petrography,'' p. 85. 
