Glacier Work. — Scott. 251 
First as to the grooves, it appears that they may in some 
cases have been pre-g'lacial in origin, and that the ice action 
was mainly that of a modifying agent. Again they may have 
been formed by the abrasive action of the rasping silt bearing 
glacial streams which always flow underneath and from the 
base of a glacier. Undovtbtedly, however, many of the grooves 
are directly responsible to the debris-charged ice for their exist- 
ence, and may be divided according to Chamberlin into two 
classes. "First, the grooves due to gouging tools, and, second- 
ly, grooves due to exceptionally long continued or succes- 
sive scoring. The former are usually limi'-ed in size and 
sharply defined, the latter wider and more vaguely delimited." 
The special gouging tools are materials such as granite and 
quartz, and the magnitude of the groove is dependent not onlv 
upon the character of the abrasive substance, but upon the 
pressure exerted and upon the relative hardness of the abraded 
surface. It is also obvious that not all original grooves in the 
softer rocks, and particularly those scorings of minor magni- 
tude, would be in e^'idence at the present time because of the 
subsequent disintegrating agencies that have acted upon them. 
The scorings have been divided into simple grooves and 
compound grooves. The former class represents the result of 
a single rock fragment, and it is worth noting that in such cases 
the cutting surface of this single fragment would be rapidly 
worn as well as the rock beneath, and give, as a result, a dis- 
tinctly different appearance to the end of the groove where 
the work began from that where it ended. The second class 
supposes a series of abrading- agents followin^r approximatelv 
the same track in succession with the result that the grooves 
are broader, less regular, and more imperfectly defined. The 
simple grooves arc thus the better indication of powerful glacier 
action. 
Many examples of grooves produced liy glacier force in 
America are recorded, among which in particular are those at 
Kelley's island, lake Erie; Amherst, Ohio; \'ictoria, B. C. : 
Cayuga lake, N. Y. ; various places in New England ; and in 
Nebraska. In the last mentioned state the grooves recently 
found in the rocks are said to be three inches across, and one 
and ()nc-(iuartcr inches deep.* 
*Jour. of Geology. 1900. 
