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elevation of the highest mountains. But still he seems uncertain if it be enough. In fact, he declares that if it were not for another factor yet unmentioned, he probably would never have brought forward the theory at all.

(9) This factor is recurrency of the cause and accumulation of the effects. And here the previous obscurity becomes intensified. I have read and re-read this part without being able wholly to understand him. He seems to think that when expansion had produced elevation, the mountain thus formed would not come down again by cooling and contraction; but on the contrary would wedge up by normal faulting and set in its elevated position. Afterward, by new accumulation of heat, another elevation and setting would take place and mountain grow higher, and so on indefinitely, or until the store of heat is exhausted. Therefore he characterizes his theory as that of "Alternate expansion and contraction," or again as that of "Cumulative recurrent expansion."

Such is a very brief, perhaps imperfect, but I hope fair outline of Reade's theory. It seems to me that there are fatal objections to it. These I now state.

Objections.—1. The first is inadequacy to account for the enormous foldings of the mountains especially when there is no granite axis to fold back the strata. It is true that Mr. Reade makes comparison between his own and the contractional theory in this regard, and seems to show the much greater effectiveness of his own. This may be true if we accept his premises and compare equal areas in the two cases. But the contractional theory draws from the whole circumference of the earth and accumulates the effects on one line, while in Reade's theory the expansion is, of course, very local.

2. But the fatal objection is that brought forward by Davison. It is this: sedimentation cannot, of course, increase the sum of heat in the earth. Therefore the increased heat of the sediments by rise of isogeotherms, must be taken from somewhere else. Is it taken from below? Then the radius below must contract as much as the sediments expand and therefore there will be no elevation. Is it taken from the containing sides? Then