276 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 26, 



In a similar case the transit of winds over extended sandy plains 

 leaves behind wave -like elevations in the form of sandy dunes. I 

 remember at a very early period of life having my attention strongly 

 fixed upon the curious gyration of very fine sand acted upon by a 

 continuous breeze. 



Upon a level plain of several hundred feet in length and breadth, 

 covered with a thin layer of very fine sand, I observed a series of 

 little vortices, each about 6 inches in height, all revolving rapidly 

 about their axes in the same direction. Each after the lapse of a 

 short time disappeared, and others continually arose. Unfortunately 

 I did not observe the character of the surface of the sand over 

 which these miniature whirlwinds traversed. 



I now return to the second theory — that of the rapid elevation of 

 a group of islands above the level of the sea at several distant in- 

 tervals of time. If this view of the subject is adopted, it becomes 

 necessary to assign a cause capable of producing such an effect. 

 Many years ago I had arrived at such a cause, to which I will now 

 refer, although I do not think it the true cause of these parallel roads. 



During a visit to Naples, in the early part of the year 1828, I 

 had an opportunity of examining the remarkable changes of level 

 which had taken place in the Bay of Naples, and in the sur- 

 rounding country, more especially those indicated by the remains 

 of the Temple of Serapis, which greatly stimulated my curiosity 

 to inquire into their causes. I had also descended into the crater 

 of Yesuvius, then in a state of active eruption, and measured a base 

 of 340 feet, by which I ascertained its depth to be at that time 

 about 500 feet. 



These comparatively recent geological occurrences within the 

 period of history formed a connecting link with far more remote 

 changes which geology had clearly established. I felt therefore the 

 want of some definite principle which should be alike applicable 

 to the whole series of geological changes. 



This led me in the latter part of the year 1 829 to a generalization 

 which I expressed shortly by calling it the theory of the change of 

 isothermal surfaces within the earth. 



At a later period, at the request of Dr. Fitton, and in accordance 

 with the wishes of Sir Henry De la Beche, I drew up a paper on 

 the subject, which was read at a meeting of the Geological Society 

 on the 12th of March, 1834. I shall only extract four hnes, taken 

 from the ' Proceedings ' of the Society. 



^* Mr. Babbage's theory therefore may be thus briefly stated : — In 

 consequence of the changes actually going on at the earth's surface, 

 the surfaces of equal temperature within its crust must be continu- 

 ally changing." (Proceedings Geol. Soc. 12th March, 1834.) 



Another important consequence necessarily results from this prin- 

 ciple — that the continual transfer of matter to different situations 

 upon the earth's surface and to different distances from its centre 

 must continually, though very slowly, alter the position of its cen- 

 tre of gravity, and also the position of its poles upon its surface. 

 Hence it follows that, in penetrating through a succession of strata 



