Rock-Weathering and Serpenti?iizatio?i. — Merrill. 245 
m Rock Deconipcsilion," the author brings up again a ques- 
tion which the present writer has often had occasion to face, 
and has vainly tried to solve in a manner entirely satisfactory 
even to himself. 
The question relates primarily to the limitation of the term 
weathering as applied to recks, and indirectly to the general 
subject of hydrometamorphism and metasomatosis as mani- 
fested in the production of serpentine. 
In my work on "Rocks, Rock-weathering, and Soils" (p. 
174), is made the following statement: — 
"The term weathering, as here used, is applied only to 
these superficial changes in a rock-mass brought about 
through atmospheric agencies, and resulting in a more or less 
complete destruction of the rock as a geological body.' as 
where granitic rocks are resolved into sand and kaolinic ma- 
terial, with liberation of carbonates of the alkalies and of lime, 
and oxides of iron. It does not include those deeper-seated 
changes taking place below the zone of oxidation and which re- 
sult mainly in hydration and the production, it may be, of 
new mineral species, as chlorite, sericite. zeolites, etc., but dur- 
ing which the rock-mass as a whole retains its individuality 
and geological identity. The distinction is not one that has 
been sharply insisted upon. and. indeed, geologists and pet- 
rologisls as a rule h.ave been extremelv careless in their use 
of such terms as alteration, decomposition, and weathering. 
The distinction drawn here is essentially that made by Roth 
(Allgemeine u. Chemische Geclogie) between Verwitterung 
and Complicirte Verwitterung. For reasons above stated and 
others given on p. 161, it seems best to limit the terms- weath- 
ering and decomposition to processes involving the destruc- 
tion of the rock-mass as a geological body, and to designate 
the purely mineralogical, deeper-seated changes, as alteration, 
which may or m-y not be due wholly to hydrometamorphism." 
This is essentially the ground taken by Lindgren also,* and 
v/hile it may be open to criticism, nothing better, so far as the 
writer is awaie. has been suggested. 
Let us take for jiurposes of discussion the serpentinization 
of the mineral olivine, as mentioned in the abstract of Mr. 
iTolland's paper. The author states (p. 31): — "In all these 
* 1 7th Ann. Rep. U. S. G. S.. 1895-6, pt. ii, pp. qo-6. 
