452 W. A. E. USSHER ON THE CHRONOLOGICAL VALUE 



Mr. H. Ellis* mentions the probability of some mammalian bones 

 and teeth washed ashore at Northam having been derived from the 

 submerged forest in that locality, Westward Ho. On Sidmouth beach 

 a stratum of blue clay is sometimes exposed after severe gales 

 through displacement of the shingle-beach; two teeth of Elephas 

 primigenius were obtained from this clay by Mr. P. 0. Hutchinsonf, 

 and are now in the Exeter Museum. In the Torbay, Blackpool, 

 and Westward-Ho forests the presence of roots and rootlets in the 

 clay leave no doubt as to the growth of the forest in situ. 



(g) The present valley-bottoms exhibit in the lower reaches of 

 the rivers considerable breadths of flat alluvial land, through which 

 the present rivers flow. The gradual upward rise of these alluvia 

 in places, terminating in gravel terraces at some feet above the 

 river-banks, connects the last stages of fluviatile action in the ela- 

 boration of the valleys. The estuarine conditions of rivers being so 

 largely dependent on slight physical and local alterations, and so 

 much influenced by human agency, it seems almost possible to ex- 

 plain such recent alterations as are evidenced by the remains of 

 Tellina, Mactra, Cardium, &c. in the alluvium of the Exe near 

 Alphington % without invoking oscillations of level. 



A somewhat similar occurrence was observed by Mr. Pengelly at 

 Torquay §. 



Erom the occurrence of similar phenomena in Cornwall I am dis- 

 posed to concede a slight amount of oscillation in the downward 

 movement which led to the submergence of the forest tracts. 



Part 2. Sequence of Deposits and oe Physical Changes. 



Owing to the want of trustworthy evidence respecting the west- 

 ward extension of the Tertiaries, and the vicissitudes experienced 

 by Devonshire during the Glacial period, its early Pleistocene geo- 

 logy is at present very indefinite. The gravel near Staple Hill (£), on 

 the Blackdowns, if not of Tertiary age, is probably the oldest deposit 

 resulting from the redistribution of Tertiary beds. 



The waterworn materials on Haldon and the Blackdowns (/3), pro- 

 bably in part resulting from a redistribution of Tertiary gravels, carry 

 us back to a period anterior to the initiation of the present drainage- 

 system. 



Erom its mode of occurrence, the clay with flints (a) evidently 

 dates its origin from a period of sufficient antiquity to allow of the 

 union of the Cretaceous deposits of the Blackdowns with Haldon, 

 and probably to a time when the Cretaceous districts abutted on the 

 slopes of the Quantocks. 



In the general Table of results appended to this paper I have put 



* Trans. Dev. Assoc, vol. ii. p. 162 ; Eep. Brit. Assoc, for 1867, Trans, of 

 Sections, p. 59. 



t Trans. Dev. Assoc, vol. iii. p. 143 (1869). 



\ Trans. Geol. Soc. 2nd ser. vol. vi. pp. 440, 441. 



§ Trans, Dev. Assoc, vol. ii. p. 164 (1867). 



