533 



slightly mixed with chalk pebbles are imbedded in sand ; and occa- 

 sionally flints are intermingled with boulders of various dimensions, 

 and sometimes unknown origin. Many of these extraneous fragments, 

 he thinks, may have been washed out of the clay ; and he shows that 

 the river valleys have been excavated through both the clay and the 

 gravel. With respect to the relative proportional quantity of each 

 ingredient, chalk flints are said to be the most numerous, primary and 

 transition rocks the next in abundance, and secondary and tertiary 

 the fewest in number; the absence of the two latter being explained 

 by their inferior hardness. 



3. Erratic blocks. — These occur in great abundance, and occasion- 

 ally of vast size. They are sometimes found in the river valleys, and 

 sometimes on the level platforms and hills. They agree in lithological 

 characters with the smaller fragments of the gavel, and are con- 

 sidered to be of the same diluvial origin ; but are so conspicuous as 

 to deserve a distinct notice. 



Lacustrine deposits. — Under this head the author alludes to the bed 

 containing freshwater shells, discovered by Mr. Charlesworth and Mr. 

 Wood on the banks of the Stour at Sutton ; and that described by 

 Mr. Brown at Copford near Colchester, which contains similar shells, 

 also bones of the ox and deer. Accumulations containing the same 

 testacea, occur at Grays near Purfleet, and at Southend in Essex, but 

 associated with rem.ains of the elephant, rhinoceros, deer, ox, bear, 

 &c. In the bed at Grays rounded pebbles of chalk occur, agreeing 

 with those found in the diluvium, and from which they were probably 

 derived. 



Causes in Action. — In this division of the memoir are described, 

 Istly, the alluvial accumulations; 2ndly, the changes in the river 

 courses ; and 3rdly, the action of the sea on the coast. In illustration 

 of the two first, Mr. Clarke enters into a discussion on the supposed 

 position of the Roman station, Ad Ansam, and the alterations which 

 must have taken place, if the site assigned to it be correct. He then 

 proceeds to the action of the tides on the cliffs. 



His first acquaintance with the coast about Bawdsey was in 1814, 

 and between that period and 1829, a battery which once stood 100 

 yards beyond the present low-watermark, has been dismantled ; and 

 the life-boat house has been three times removed, to a distance at least 

 a quarter of a mile, in rear of its original position. 



The destruction between the Aide and Bawdsey cliff during the last 

 20 years, is calculated to have been upwards of 1 00 acres ; and the 

 coast between that cliff and Bawdsey Haven, is stated to have dimi- 

 nished about two yards annually. Similar remarks apply to the cliff" 

 between the Deben and Harwich harbour, batteries and martellp 

 towers having been successively undermined. 



In 941 the church at Walton Naze was at a considerable distance 

 inland ; about 50 years since the church and burial-ground remained 

 but not a vestige of either is left. In 885 a sea fight took place be- 

 tween Alfred and the Danes at the mouth of the Stour, where the 

 shingle bank now is. Harwich is also stated to have arisen in con- 

 sequence of the destruction of Orwell, which stood on the spot 



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