ni 
ae ure 
ON THE GEOLOGY OF THE ISLAND OF AQUIDNECK. 759 
is by atmospheric erosion alone; every pebble in a gravelly soil 
wastes over its whole surfaces, so that the aggregate area of supply 
_ Whence plants can draw their nutriment is many times greater 
than if it all came from the wearing of*the bed rock. There is 
also the mingling of materials which took place during the glacial 
period, which has not been without effect in increasing the produc- 
‘tiveness of soils. This action has brought into each cubic foot ` 
of our boulder clays a great assortment of diverse materials giv- 
ing a soil ready for the nutrition of any seeds which fall upon it. 
_ However varied the demand, it would be sure to find the mate- 
tials at hand. During the glacial period there was no vegetation 
in the drift covered region for a period of time which must be reck- 
oned by thousands if not hundreds of thousands of years, so that 
the materials which came into an assimilable condition remained 
unappropriated by plants and were in a fashion stored for their 
future use; when the ice sheet passed away, the soil was left with 
= arich store of materials suitable for the nutrition of plants. It 
may be that the vigor of the carboniferous vegetation was in part 
the result of this glacial preparation of the earth’s mariage for 
vegetable life. 
The whole time of the formation of this conglomerate was a 
period of recurring changes of condition. The pebble beds alter- 
hate with sandstones and shales and occasionally with somewhat 
carbonaceous layers of slate. At one point, Wood’s Castle, on the 
- astern shore of the island, the conglomerate is immediately over- _ 
laid by carbonaceous shale with faint traces of coal plants ; above 
the coal comes a greenish shale of an unknown thickness. It may 
bt said by some that the juxtaposition of carbonaceous beds makes 
the glacial origin of the conglomerate doubtful. That this reason- 
ing would be fallacious is well shown by the fact that in New 
Zealand we have a vegetation more closely allied to that of the 
Carboniferous period than is found in almost any other region 
growing in the immediate neighborhood of the glaciers. Very 
slight changes in the conditions prevailing there might bring a 
Vegetation of palms and tree forms upon the débris of the ice 
tre. 
- Streams. 
_ The history of these conglomerates would not be complete with- 
me Out a consideration of the often noticed and much misunderstood 
: compression of the pebbles. The pebbles which make up a large 
__ Part of the conglomerate which lies to the south of Easton’s Beach 
