1887] | The Materials of the Appalachians. 1059 
suggestion which I wish to make. It may be of some use in 
explaining the phenomena, and it may not. I am disposed to 
attribute it to the tide, whose forced wave, sweeping every day 
over the successive ridges or through the successive archipel- 
agoes which I have described, tore away the rocks and swept 
- the fragments westward, rolling them over and over against one 
another until they were ground to pebbles and to sand, The 
_tide-wave reaches the bottom of the deepest water, and is not a 
Mere superficial current. Its motion is incessant, twice a day, 
and not occasional as that of the storm-wave. Finally, its di- 
tection in this region was westward, and it is a fact of no little 
- Significance, in this connection, that, so far as we can determine, 
all the material of these four sandstones has travelled westward. 
_ These considerations united induce me to believe that the 
-tide-wave was the chief agent in their formation ; that, rolling, 
às it did, every twelve hours from the East into the midland 
ocean of North America, through the successive archipelagoes 
 Orreefs which I have here attempted to describe, it acted as a 
Sinding and transporting engine of transcendent power to 
-fshion and to carry the sand and pebbles of which our great 
- Songlomerates consist. 
__ There is nothing, so far as I am aware, in the rocks that is 
incompatible with these views. It is well known that the con- 
i glomerates are thicker and coarser in the East than in the West, 
, and accordingly in the West this material constitutes 
whole mass of the rock. 
Une other point should be at least alluded to. Recent Te- 
‘Starches have rendered it probable that this great grinding 
i , Tegarding the origin and formation of the Conginmnm E 
ennsylvania, prove to be of any value, they may por r 
on the moot question of the antiquity of the Asians 
