18 NEW YORK STATE MUSEUM 
AN ATTEMPT TO DETERMINE THE ORIGIN OF THE 
GLACTAW MORAINE Sep ROMA SMUD Ya Ol iGileN@WNG 
BOULDERS 
If a boulder buried in a moraine or left standing alone as a re- 
sult of outwash, can be identified by its mineral structure, its general 
petrological character, or if it should contain fossils with any known 
outcrop of rocklike character, a clue is at once afforded to the direc- 
tion and distance through which this boulder has moved. It happens 
frequently in the study of such boulders from the fossiliferous rocks, 
that the fossil contents afford evidence of the approximate origin of 
the transported block. What is true of morainic boulders is equally 
true of outwashed gravel from deposits of till. But in a state like 
New York where the fossiliferous outcrops run for the most part 
in an east and west direction, except as they bend south and south- 
eastward along the Hudson valley, such clues as the fossils afford 
are not very exact, in view of the fact that the sedimentary strata 
may hold their lithological and fossil characters over long distances. 
As a striking illustration of this fact we may cite the fossil-bearing 
pebble beds from about Fort George, New York City. These are 
full of paleozoic fossils which have evidently come from the north 
and northwest, but from just what points they have been derived or 
how far they have been transported is still a matter of uncertainty. 
Identity of petrographical structure in crystalline or igneous rocks 
seems to be of somewhat more reliable character and Dr A. C. Gill 
of Cornell University has interested himself in the effort to establish 
the identity of such crystalline boulders with their parent ledges, 
basing his observation on the test of intimate microscopic petrology. 
It is probably true that in a country like this, whose rock outcrops 
have been extensively ground down and quite as extensively buried 
by glacial débris and soil, the chances for such positive identifications 
must always remain remote and must depend in large degree upon 
the identification being founded on a rock mixture of unusual char- 
acter. Doctor Gill has, however, gone far enough to bring out in 
certain cases a very definite probability in favor of far-traveled 
glacial blocks whose place of origin can be located with some degree 
of reliance. 
These are very suggestive operations and in order to test out this 
procedure more fully, a field effort has been made to assemble addi- 
tional data that may eventually lead to further identifications of this 
kind. In selecting certain areas in the eastern part of the State, 
