1G2 Mr. S. V. Wood on the Form and Distribution of the 



elevations appear to have emanated from foci of force, where the 

 volcanic action was the most exerted, or at least where it found 

 the least resistance, and produced the greatest dislocations ; in a 

 word, the upheaval (however prolonged) of mountain chains, has 

 converted large tracts falling within their influence into dry land. 

 Now if we can in imagination remove the inequalities produced 

 by any volcanic upheaval, and by so doing restore the surface as 

 it existed before such upheaval took place, it is clear that we 

 should remove the chief difficulty in arriving at a correct view of 

 the relative configurations of the land and water during the an- 

 tecedent period. 



Again, consider how during every successive geological epoch 

 since the close of the palaeozoic period, but more particularly 

 during the Jurassic and cretaceous epochs, the sea over the 

 south-east of England and north of France has returned to the 

 basin occupied by it during the immediately preceding geological 

 period, where no anticlinal has interfered to change the relative 

 levels of the surface : thus we see the outcrop of the Jurassic and 

 cretaceous formations, and even of the older tertiaries over this 

 district, forming a series of concentric rings, the newer formation 

 lying within the older*. If we can so plainly perceive this where 

 powerful dislocations have taken place subsequent to the older 

 tertiaries, which have not only interfered with the old and gra- 

 dually narrowing sea-basin of the secondary and older tertiary 

 seas, but reversed the very inclination of the surface, so that the 

 land, from which came the sediment that supplied the clays and 

 limestones of those ancient formations, now falls away to the 

 west under the deepening water of the British Channel towards 

 the Atlantic, how much more plainly ought we to perceive it in 

 those parts of the world where the strata have remained over 

 great areas undisturbed by anticlinals since they were deposited, 

 as in Russia, North America, &c, places in which, if the tracts 

 were now sufficiently depressed, the ocean would again wash 

 almost the same coast-line which it did in the secondary periods. 

 Even in England, which is a geological microcosm, and where a 

 more regular succession of strata exists than in any other known 

 tract of equal size, there is by no means that overlay of successive 

 deposit^ to the extent that apparently exists, since not only does 

 the whole Jurassic series thin out as it recedes from those ancient 

 lands the drainage of which formed the sources whence was de- 

 rived the sediment of its deposits f, but the basins which the 



* It is intended only to be said that this is the result of the geological 

 changes since the commencement of the secondary period, broadly con- 

 sidered, as it is well understood that numerous local interruptions oc- 

 curred in this order of events, causing local absence of some of the subor- 

 dinate divisions of the several secondary groups. 



t See Hull, Quart. Journ. Geol. Soc. vol. xvi. p. 63. 



