366 Rev. W. B. Clarke on the Geological Structure 



tional quantity of each ingredient^ the chalk flints are the most numerous^ 

 primary and transition rocks the next in abundance, and secondary and ter- 

 tiary the fewest in number ; the absence of the latter being easily explained 

 by their inferior hardness. At Stratford St. Mary, and East Bergholt, I have 

 collected specimens of nearly every rock in England to the N. W. of Suffolk. 



3. Erratic Blocks. — These bowlders consist of granite, porphyry, basalt, 

 limestone, and the sandstones of the various formations, and occur in great 

 abundance, and occasionally 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 gravel, and 

 are considered to be of the same diluvial origin, but are so conspicuous as to 

 deserve a distinct notice. Among numerous other localities I may mention 

 Copdock, East Bergholt, the valley between Thorington Street and Scotland 

 Street, near Stoke ; and at Flatford Mill in East Bergholt parish. 



Lacustrine Deposits. — Under this head 1 must notice the bed containing 

 freshwater shells, discovered by Mr. Charlesworth and Mr. Searles Wood * 

 on the banks of the Stour at Stutton, and that described by Mr. Brown, at 

 Copford near Colchesterf, which contains similar shells, also bones of the Ox 

 and Deer: accumulations at Grays near Purfleet and at Southend in Essex, 

 inclosing the same teslacea, but associated with the remains of the elephant, 

 rhinoceros, deer, ox, bear, &c. have been described by Mr. Morris;};. 



Causes in action. — Under this head 1 shall confine my observations to the 

 action of the sea on the coast, the changes produced by fluviatile accumula- 

 tions being of little importance. My first acquaintance with the coast about 

 Bawdsey was in 1814, between which period and 1829 a battery which stood 

 100 yards beyond the present low-water mark has been dismantled, and the 

 life-boat house has been three times removed to a distance of a quarter of a mile 

 at least in rear of its original position. The destruction between the Aide 

 and Bawdsey Cliff during the last twenty years is calculated to have been up- 

 wards of 100 acres, and the coast between that cliff and Bawdsey Haven is 

 said to have diminished about two yards annually. Similar remarks apply to 

 the cliff between the Deben and Harwich Harbour, batteries and martello 

 towers having been successively undermined. During the time of the Romans 

 there was a castle in the cliffs at Felixstow, built by Constantine to guard the 

 entrance of Orwell Haven. Holingshed says the earl of Leicester landed 

 therein 1173; but in 1176, Henry H. overthrew the castle. In 1722 the 

 ruins extended 100 feet in length, were 5 feet high and 12 feet broad ; pebbles 



* Mag. Nat. Hist. vol. vii. p. 274. t H^id. vol. vii. p. 436. 



X Ibid. vol. ix. p. 261. See also liis paper on the deposits in the valley of the Thames, M.N.H. 

 vol. ii. N.S. p. 539. 



