Mr. Webster on the Strata lying over the Chalk. 247 



If we consider that the flinty chalk is somewhat above the level 

 of the sea at Woolwich and Gravesend ; that it dips under the Isle 

 of Sheppey and disappears ; that at Margate it has been so elevated 

 that a considerable part of the lower chalk is now seen, the whole 

 of the upper or flinty chalk being gone ; that at Dover it rises to a 

 vast height ; that on the north side of the Thames it appears at 

 Purfleet opposite to Gravesend, but immediately disappears to rise 

 no more on the coasts of Essex and Suffolk. — If we reflect on the 

 rapid dip of the chalk at the Hog's back, between Guildford and 

 Farnham, with the many hills and hummocks of chalk to be seen in 

 the counties of Suffolk, Norfolk, &c. we may perceive evident 

 proofs of the great irregularity of the ancient surface of this stratum, 

 and a part of the elements which may enable us to trace the 

 limits of the land and sea at that period. 



In speaking of the formation of the gravel, the probable mode 

 has been detailed, by which the mountains of chalk originally 

 appearing above the sea may have been worn away, cliffs have been 

 formed, and the flints broken and rounded into pebbles. Of the 

 early existence of this process, we have seen proofs in the vertical 

 bed of pebbles of Alum bay, and in those frequently found in the 

 sand of the plastic and blue clay in many other places. And also 

 in the lower beds of the calcaire grossier of the basin of Paris. 



We have seen also that the extraordinary event of the elevation 

 or subsidence of the chalk of the Isle of Wight and Dorsetshire 

 must have taken place after the deposition of the great stratum of 

 blue clay. 



A change of this kind, of which we have no parallel in human 

 record, it would be in vain to endeavour to account for ; but it 

 must have been an event of itself sufficient to produce great changes 

 in this part of the globe, and must have been accompanied by the most 



