382 The American Geologist. December, 1902. 
igin, and lias seen within it a record of chemic activity vary- 
ing through the ages with changes in atmospheric conditions 
and cHmate ; Pumpelly has seen within it a possible source of 
vast seolic deposits ; Julien has ably set forth the influence of 
the humus acids in decomposing rocks and producing soils, 
and has. like Hunt, seen within the products a record of var- 
iable activity in the rock destruction and considerable changes 
in the climate of the earth during the geologic periods ; Hil- 
gard, Shaler and others have investigated the products of rock 
decay as the most important source of soils ; Chamberlin and 
Salisbury have made a classic study of the origin and physical 
compodtion of the residuary clays and loams of a definite ter- 
ritory and Rusfell has summarized the work of his predeces- 
sors, pointed out that the products of rock decay vary in vol- 
ume with the latitude, and inferred that they represent secu- 
larlv constant activity in the rock-destroying process. The 
local characteristics of the extensive mantle of rock debris 
within this country have also been set forth by a score of ge- 
ologists in half the states of the Union. 
Perhaps because of its universality in many lands and its 
prevalence in nearly all, the product of rock decay has no 
commonly accepted appellation. Pumpelly indeed groups the 
phenomena as "residuary products of a secular disintegra- 
tion" ;* Chamberlin and Salisbury combine them as "residu- 
ary products" ;t and Russell speaks of "residual clay." "res- 
idual deposits," "residua," etc ;$ but the expressions are man- 
ifestlv employed as descriptive terms rather than specific 
appellations. Broadhead designates such material as "local 
drift, "§ and Kinahan applies the term "meteoric drift"; II but 
these expressions, too, are employed rather in a descriptive 
than in a denotative way, and moreover they are misleading 
in that, where typically developed, the materials are not drift- 
ed. Many varieties of rock debris indeed have descriptive 
names: — "adobe," "gumbo" (applied to disintegrated Cre- 
taceous and Tertiary shales as well as to a Pleistocene depo.s- 
it), etc., are common terms in this country; "terra rossa" is 
* Am. Jour. Sci., 3d Ser., vol. 17, p. 135. 
t Sixth Ann. Rep. U. S. Geol. Survey, 1885. p. 230. 
t V. S. Geol. Survey Bull. 52, pp. 13, 23, and elsewhere. 
§ Geol. Surv. Mo., 1874, pp. 64, 98, and elsewhere. 
II /our. of the Royal Geol. Soc. of Ireland, 2d ser., vol. 4, part 3, pp. 115-1 21 
