WOODWORTH: GEOLOGICAL EXPEDITION TO BRAZIL AND CHILE. 7/7 
Where this type of pebble occurs on the surface of the ground at the 
present day as it does in the glaciated regions of eastern North America 
it might possibly be interpreted as owing its conchoidal fractures to 
the work of aboriginal man, but when firmly embedded in the glacial 
till of that district or in the tillite beds of Brazil no one would presume 
to connect it causally with human art. These crushed and bruised 
rock fragments with their sides well striated are common in south 
Brazil and along with other striated pebbles argue for the crushing, 
bruising action of a thick body of ice such as a glacier would afford. 
Even where stones of this type of contour occur isolated in fine shales 
into which they have been dropped from floating ice, the evidence as 
to their original handling by glacial action is equally good. 
Classification of Lithified Glacial Deposits and Derived Sediments.— 
‘The lithological classification of sediments takes no account of genesis, 
its names, somewhat more carefully defined than in common usage, 
express ideas concerning the size of constituent particles, as in the 
terms conglomerate and sandstone; or designate vaguely a mode of 
fracture, as in shale with an understood composition of particles too 
small to be distinguished by the unaided eye. This simple primitive 
classification embraces all lithified glacial deposits when used with 
proper qualifying terms. The glacial deposits, so far identified, have 
given rise to two independent terms, boulder-bed and tillite, the first 
of which is conveniently vague, except for its reference to boulders, 
while the second covers a wide range of commingled rock fragments 
and particles having this in common that they were deposited by the 
agency of glacial ice. The study of modern glacial deposits would 
lead us to expect among ancient glacial deposits the lithified counter- 
part of each product of glacial action and the glacio-natant waters. 
Tillite, as consolidated till, would naturally be applied to all un- 
stratified, unassorted deposits due to the direct agency of a glacier. 
The term thus is applicable to the rock of fossil moraines whether 
frontal, or ground-moraine, and to fossil drumlins. These varieties 
of tillite, since they are distinguished by topographic form, will not 
in the nature of the case take petrographic designations. The same 
remark applies to the assorted glacial gravels and sands forming the 
group of kames, eskers, and proglacial deltas, or gravel- and sand- 
plains. For their petrographic designation there is no distinctive 
term correlated with till and tillite. The coarser deposits are in- 
cluded in the conglomerates and the finer among the sandstones. 
The glacial rock-flours or clays, normally unweathered, finely divided 
clastic materials of complex mineralogical composition, often feldspa- 
