Trains of Boulders, in Berkshire, Mass. 391 
at all periods of geological time, merely supposes that, at the 
epoch of the drift, the polar half of the northern hemisphere 
was the theatre of violent, and perhaps frequently repeated, 
movements of the earth’s crust, each particular disturbance 
emanating, probably, from a different local region. These 
disturbances, which are conceived, by Von Buch, De Beau- 
mont, Hopkins, De la Beche, Sedgwick, Phillips, and other 
distinguished geologists, to have been of the nature of simple 
paroxysmal elevations, and by ourselves, to have consisted in 
an energetic and extensive undulation of the crust of the 
earth accompanying each sudden rise, are deemed suflicient 
to have caused a rush of the northern waters over all the 
higher latitudes of Europe and North America, covering the 
surface with an almost continuous sheet of gravel and bould- 
ers, and polishing and scoring the whole rocky floor. 
“The chief cause of hesitation, with many minds, in em- 
bracing a theory so much in harmony with the general physi- 
cal history of our globe, bas arisen from their not recognizing 
à force sufficient to dislodge and sweep onward blocks of the 
huge size which we sometimes encounter, or to drive the 
detrital matter up and over the high mountain barriers, across 
Which, by some process, it had travelled. So long as no de- 
finite estimate had been made of the velocity of the current 
which Would result from a given amount of paroxysmal eleva- 
ton, such a distrust of the energy of diluvial waters was 
natural and prudent; but we are in possession of facts and 
Seneralizations calculated greatly to exalt our conceptions of 
power. 
_ “Tt has been shown, by Mr. Hopkins, of Cambridge, reason- 
g from the experimental deductions of Mr. Scott. Russell 
upon. the properties of waves, that * there is no difficulty us 
accounting for a current twenty-five or thirty miles an hour, if 
We allow of paroxysmal elevation of from one hundred to two 
hundred feet;" and he further proves that a current of twenty 
San hour ought to move a block of three hundred and 
‘wenty tons, and since the force of the current increases in 
