534 



called the West Rocks, and was overwhelmed by an inroad of the sea, 

 since the Conquest. During the period^ however, that these destructive 

 changes having been proceeding on one side of Harwich harbour, 

 sandbanks have accumulated at another, and compelled the Stour 

 and the Orwell to open a new line of communication with the sea. 



The author then gives the following conclusions as deducible from 

 the statements in the body of the memoir. 



1 . The substratum of the whole of Suffolk, Norfolk, and Essex is 

 chalk, which appears to have been dislocated and worn into deep hol- 

 lows by the action of water, previously to the commencement of the 

 tertiary era. 



2. On this abraded surface the plastic clays and sands were 

 formed, but not over the whole area. 



3. Partly on these beds and partly on the chalk, the London clay 

 was then deposited, but to no very great thickness. 



4^ Upon the London and plastic clays as well as the chalk, the 

 crag was next accumulated in sandbanks, produced by the tidal waters, 

 and around projecting masses of chalk. 



.5. While the crag still lay beneath the sea, a violent catastrophe 

 broke up many of the secondary strata, from the chalk to the lias in- 

 clusive, and the debris thus produced, together with numerous masses 

 of ancient rocks, was spread by a rush of water over the surface of the 

 tertiary formations and the chalk, in some places to a depth of 400 

 feet, constituting the beds of drift clay,&c., which occupy so great an 

 area in Suffolk. 



6. Previously to this diluvial action, and after it, the rivers of the 

 then dry land bore to the sea, animal and vegetable remains, vestiges 

 of which occur on the Norfolk coast and elsewhere. 



7. The climate of this part of the globe was at that era different 

 from the present. 



8. After this period, and probably in prolongation of the first great 

 catastrophe, a series of shocks acting from below, shattered the surface 

 and gradually elevated the whole district, till the crag attained tlie 

 height of nearly 100 feet above the level of the seaj and by this 

 movement were produced the valleys or lines of fissure, through which 

 the drainage of the county is effected. 



9. No great convulsions have since taken place. 



1 0. By the action of springs, and the constant battering of the sea, 

 the superficial contents of the London clay and crag have been re- 

 duced several miles, vestiges of their former extent being traceable in 

 rocks and sandbanks nearly always submerged. 



11. By the set of the tides vast accumulations of shingle and sand, 

 have been formed at projecting points, protecting in some places the 

 cliffs from further destruction ; but at Harwich harbour they have 

 blocked up the ancient estuary, and compelled the Stour and Orwell 

 to form a new outlet. 



1 2. The average amount of annual degradation of the coast is about 

 two yards in breadth ; and in consequence of the confirmation of the 

 ridges of crag and London clay, the cliff's will gradually diminish into 

 a low sandy shore. The period estimated by Mr. Clarke for effecting 

 this destruction is another century. 



