bearing on theoretical Speculations. 21 



the middle of the tertiary period. The observations as yet 

 made on that great chain are scarcely sufficiently full or ac- 

 curate to determine whether that elevation was at once effected 

 by a single period of convulsion, or gradually during many 

 such successive periods * ; but the latter opinion appears far 

 more probable, and seems most agreeable with what is hitherto 

 known. It is scarcely necessary to add, after our introductory 

 observations on this article, that the method of determining 

 this point would be, carefully to examine the junction of the 

 different constituent formations, and carefully to examine how 

 far they were conformably affected by the same convulsions. 

 On this point the sections published by Ebel are scarcely 

 sufficiently minute or accurate to afford the requisite informa- 

 tion. In those of Mr. Murchison we find the tertiary conglo- 

 merates, &c. of Gossau overlying unconformably : but as on 

 the Italian side the vertical beds of scaglia (equivalent to 

 chalk) and of the succeeding tertiary deposits seem quite con- 

 formable to the older formations, we have here convulsions 

 even as late as the tertiary period, compared with which, every 

 thing of actual occurrence, the elevation of Jorullo, &c. dwin- 

 dles into insignificance. 



In our own island the elevation of the central range of 

 chalk in the Isle of Wight, and that of the Isle of Purbeck, 

 must be referred to the same period. If by examining the re- 

 lations of the contiguous formations it appears to have been the 

 result of a single convulsion, limited to a period subsequent 

 to the lower tertiary deposits and antecedent to the higher, 

 this single convulsion, thus limited to a point of time geologi- 

 cally, affects a district nearly sixty miles in length (from the 

 east of the Isle of Wight to Whitenore Point, east of Wey- 

 mouth) : and if we take into account the thickness of the strata 

 moved, and the extent of their dislocation, it must have occa- 

 sioned an angular movement throughout the whole of this 

 space averaging more than 1000 feet. I could only desire 

 the advocates of " actual causes," energizing with their pre- 

 sent degree of power, to show me a single instance of any 

 effect produced by them in the least comparable with this. 



VI. The analogous rocks belonging to the different succes- 

 sive formations present a regular gradation in texture and 

 consolidation: the earliest being the most crystalline and 

 compact; and these characters becoming regularly less and 

 less in the successive deposits, as they are more and more re- 



* Elie de Beaumont, in his very valuable memoir " Epochs de Souleve- 

 ment" shows the Alps south of Savoy to have been elevated at an old 

 tertiary period, the eastern Alps at a much newer. 



cent. 



