182 
Fic. 12. Cut in a glaciated region (Helderberg Mts., Albany Co., N. Y.) 
showing unconformity between glacial soil and the underlying bedrock, the 
soil not having been derived from the underlying rock. (Photo by E. J. 
Stem. Courtesy N. Y. State Museum.) Cf. Fig. 13. 
Bronze tablets have been placed on several of the larger boulders, 
telling their composition and the location of the rock ledges from 
which they were probably broken off by the glacial ice itself or the 
forces of weathering, before they started on their long (and shall 
we say * final”) journey to the Rock Garden and boulder bridges 
of the Brooklyn Botanic Garden (Higs. 11 and 22 
The Time Element 
How long a time was required for the transportation of the 
Botanic Garden boulders from their points of origin to what is 
now Long Island? This, of course, depends upon two factors: 
the distance travelled and the rate at which the ice advanced. 
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