War 
were found. The big one on Rock Island was moved to the 
Island from farther north. Some of the material south of the 
bridge may possibly have been laid down under water, in an 
ancient local lake or pond, for it 1s stratified, with the coarser ma- 
terial at the bottom, just as always occurs when a mixture of 
materials of various degrees of coarseness and fineness is allowed 
wanes it m tee rey gf pea Net: 
ae EE — ie a othe 
“ae 
i 
ou 
amy 
Irrc. 5. Glacial boulders uncovered during grading operations in front of 
the Laboratory Building, Brooklyn Botanic Garden, 1931. (7326) 
to settle (by sedimentation) in more or less quiet water. On the 
whole, however, the material of the frontal apron or “ outwash 
plain’ on Long Island is composed of cross-bedded material de- 
leslie on a water-soaked plain. As a rule, the material of the 
“back bone’ ridge is not stratified. Gravel often overlies the 
finer sand; finer clay may lie underneath the gravel. Obviously, 
this material was not laid down under water. 
The Boulders Were Brought Here 
Moreover, it seems quite clear that many of the larger boulders 
could hardly have been transported by flowing water alone—yet 
transported they must have been, for they must have been derived 
from bedrock and brought by some agency to their present resting 
places. In recognition of that fact the rocks are commonly called 
erratic boulders (boulders that have “ wandered”). Whence did 
they come, and how? What was the origin of the “back bone” 
