Apparent objections to the Glacial Theory. 299 



exfoliate and split into fragments of various magnitude, and these 

 fragments yielding to the force of the waters which were thus sud- 

 denly displaced, would have been hurried off by the retreating waves 

 to the lower levels. This reasoning seems in some measure to 

 derive support from the facts observable, whenever in modern times 

 an outburst of volcanic matter takes place from beneath the sea ; 

 numerous instances are on record of islands suddenly appearing 

 above the waters, but these have almost invariably disappeared 

 again after a short time, from their summits having been swept 

 off in fragments caused by the sudden refrigeration and splitting of 

 the surface, as the heated matter came in contact with the superin- 

 cumbent ocean. The ruggedness of primary ranges is therefore 

 easily accounted for by the sudden cooling of the surface when in a 

 state of intense heat, and by the immediate denudation attendant on 

 the passage of the tumultuous body of waters displaced by the 

 movement. The step-like appearance of trappean rocks would, in 

 like manner be caused by the sudden refrigeration of surface induc- 

 ing the rock to split into cuboidal masses, and the denudation of 

 this fractured surface would therefore give the step-like appearance 

 alluded to. This may perhaps be admitted as a satisfactory expla- 

 nation of the phenomena apparent in these formations, and coupled 

 with the subsequent tumultuous action of the waters on the newly 

 detached fragments may enable us to arrive at some explanation 

 of the reason, why ancient detritus is almost invariably rounded and 

 worn. Had the action of the displaced waters been no greater 

 than that exercised by the transient passage of a flood over the lower 

 lands, doubtless the effects attributable to it would have been insuf- 

 ficient to account for the polishing and rounding of erratics, but we 

 must not be blind to the fact, that a sudden and violent outburst of 

 large tracts of land, or of mountain ranges from beneath the sea, 

 would have given rise to waves which would not only have acted 

 with an intensity of force of which we can perhaps form no just con- 

 ception, but likewise that their action on the land would have been 

 of long continuance. " The vibration of the sea produced by the 

 great Lisbon earthquake of 1755, threw a wave sixty feet high on the 

 coast of Cadiz, and one eighteen feet in height on the island of 

 Madeira. The area agitated by this earthquake comprised a large 



