Editorial Comment. 209 
in the knolls was eroded from the ridges by the stream itself. 
Whether this material had previously been loosened and brok- 
en up by the action of the ice is immaterial to my present 
purpose, which is to prove that the streams did not flow at a 
level above the tops of the highest hills on which the ice-sheet 
rested. In nearly all cases where a gravel deposit occurs with- 
in two miles west of a prominent rock ridge, it contains beds 
of coarse pebbles and cobbles which are almost exclusively of 
Galena limestone. 
{To he continued.] 
EDITORIAL COMMENT. 
An important aid to the investigator and general 
STUDENT. 
"Where has this subject been-previously treated?" is a ques- 
tion perpetually recurring to the investigator, and the answer 
is never satisfactory. Not only is the body of geological lit- 
erature so large that no individual can cope with it, but its 
bibliography has not been successfully attempted by any or- 
ganization. Nevertheless, there are numerous works, such as 
partial bibliographies, indexes to libraries and serials, and 
reviews of special subjects, which may be of great use to the 
student if only he is aware of their existence and knows where 
to find them. A real need has therefore been met by the 
bibliographical committee of the International Congress of 
Geologists, in preparing its "Catalogue des bibliographies geo- 
logiques," which gives a classified list of all partial bibliogra- 
phies of geology known to exist, either in print or manuscript. 
How well the need is met can not be told until it has been 
practically tested by use, but the volume bears witness to the 
most earnest and painstaking endeavor, and those who exam- 
ine it can hardly fail to be astonished at the very large num- 
ber of existing sources of information as to the extent and 
character of the literature of geology. Emm. de Margerie and 
his colleagues on the committee have assembled no less than 
3,918 separate titles of bibliographies and allied works, and 
have described them with such fullness as to make a volume 
of 750 pages. Some of the works entered, like the catalogue 
of the Royal Society of London, contain lists of publications 
of individual geologists; others are bibliographies of partic- 
