MUSEUM OF COMPARATIVE ZOOLOGY. 187 
necessary that there should be a sufficient distance between the selected 
locality and the sea to afford a chance for the display of a bowlder 
trail of such length as to afford indications of value. After much pre- 
liminary search of various localities in New England, I found that the 
boulder train from the so called Iron Hill in Cumberland, R. I., pre- 
sented by far the most satisfactory basis for the proposed study. 
GENERAL DESCRIPTION OF THE TRAIN. 
The accompanying map will afford the reader a sufficient idea-as to 
the geographical conditions of the district in which the trail from the 
Tron Hill lies. It will be observed that the iron deposit is situated in the 
town of Cumberland, which lies on the eastern margin of the valley of 
the Blackstone River, at a point about fifteen miles north of Providence, 
R. I. Although the contour map which accompanies this report, and 
which is reproduced from the plates prepared by the U.S. Geological 
Survey, will afford an excellent idea of the topography, the scale on 
which it is printed is somewhat smaller than is desirable for the com- 
plete display of the matter with which we have to deal. It would have 
been possible, from the original maps of the Survey, to have made this 
illustration on a more considerable scale, but the chart would have then 
been too large for convenient use. 
It will be observed that, except for the occurrence of a few somewhat 
isolated hills, the reliefs of this district have no great height. They 
rarely, indeed, exceed one hundred feet of elevation above the neigh- 
boring valleys. For about thirteen miles from its point of origin, this 
glacial trail lies upon a surface of bed rock of varied hardness, which 
still retains in good part the topography given to it by erosive agents 
which operated before the advent of the last Ice Age. The boulder 
clay or ground moraine of which the train forms a part is, except where 
it crosses these ancient valleys, usually not more than ten feet thick. 
It is likely that in this district there may be many deep valleys in the 
bed rock which have been entirely effaced by the thick deposits of drift 
which mantle this part of the coast between Valley Falls and Aquidneck 
Island. On that island the bed rock is again near the surface, the drift 
being rather more than fifteen feet in average depth, and except next the 
shores, where some washed drift occurs, consisting altogether of boulder 
clay. In this part of its course the movement of the glacial stream 
which bore the material deposited in the train may have been somewhat 
guided by the long ridge which forms Aquidneck Island, and by the 
