126 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
phenomena may occur in lakes under favorable conditions. River 
ice may also inclose more or less coarse stony waste, which the streams 
may deposit along their courses or may bear away to some lake or to 
the ocean. Again, trees, uprooted and borne along by floods or under- 
mined by wave action at the base of cliffs that they surmount, may 
embrace among their roots large fragments of rock, which may thus 
be floated away and deposited among finer sediments. Moreover, 
the masses thus transported and deposited may already have been 
marked with striations, due to the jamming of ice cakes either along 
shores or against river banks. 
The mere occurrence, therefore, of striated boulders among fine 
bedded lacustrine or marine sediments cannot be regarded as indubi- 
‘table evidence of glacial action. The relative number and shape of 
the fragments and the character of the striations must be considered. 
In the case of fragments distributed by icebergs, the shape is generally 
that of pebbles embedded in boulder-clay — faceted, with snubbed 
ends and rounded edges — and the striations are commonly more 
strongly marked parallel to the length of the fragment, though two or 
more directions may be indicated on the same stone. Occasional 
larger masses not so shaped and striated might occur, for it is possible 
that an iceberg might carry some masses that had fallen on the sur- 
face of the glacier and had not been subjected to movement under the 
pressure of superincumbent ice. In the case of debris distributed by 
shore or river ice the shape of the fragments would generally be that 
of beach shingle or of stream pebbles — rounded or subangular — 
and the striations would not so commonly be in the direction of the 
long axis of the pebble. Here again, larger or more angular masses 
might occasionally appear, for fragments freshly broken from the 
parent rocks might be embedded in ice and floated away before they 
were shaped by water action. In the case of materials distributed by 
floating trees the same comments as to shape and striations would 
apply as in the case of shore or river ice-rafted waste. The number of 
fragments thus distributed is, however, probably much less than 
that disposed of by any of the above noted methods. 
Deposits assigned to glacial action in ancient periods occur in a 
number of countries. These will now be described in order to obtain 
the criteria by which their glacial origin was determined. 
:—India. At the base of the Gondwana system and resting 
unconformably on older Palaeozoic rocks there is a group of peculiar 
sediments discovered in 1856 by W. T. and H. F. Blanford and named 
by them the Talchir group. These rocks have been described by 
