AUSTEN — TERTIARY DEPOSITS OF THE SUSSEX COAST. 



45 





> 



O 



S - 





PQ 



Caen and the Orne* consists almost exclusively of 

 waterworn quartzose and old Silurian rocks. 



§ II. Superficial Detritus of the East End of 

 the Channel. 



Dorset. — Detritus caps the summit-levels of all 

 the hills which extend from Devonshire into 

 Dorset ; it presents a twofold divisionf — the lower 

 consisting of more irregular materials than the 

 other, with a marked line of separation, and with 

 this further characteristic for the upper portion, 

 that it contains rounded pebbles of white quartz, 

 porphyry, and granite. It is only in the valleys 

 that those local accumulations are met with which 

 include the remains of the large mammalia. The 

 whole of these high-level gravel-beds were spread 

 out before the surface of these counties was in- 

 tersected by its present system of deep combes and 

 broad valleys, showing the vast lapse of time which 

 separates these two accumulations. 



Passing thence into the tertiary area of Dorset 

 and Hants, we find the vast amount of detritus 

 which covers the surface strongly marked from the 

 coast as far inland as Salisbury. For the purpose 

 of comparing this tertiary area with that beyond it 

 on the west, the geologist cannot do better than 

 follow the coast-sections from Portland and Wey- 

 mouth Bay, by Studland, and thence to the Solent;];. 

 Poole Harbour is partly due to denudation and 

 partly to depression. On the east is high ground, 

 which at a spot a little to the right of the road lead- 

 ing to Bournemouth will be found to be capped by 

 an isolated mass of gravel, in which are several very 

 extensive pits. This accumulation differs in many 

 respects from the ordinary gravel-beds of the di- 

 strict, the most important point with reference to 

 the present sketch being the presence of water- 

 worn specimens of white quartz, granite, and por- 

 phyry. It is very probable that similar gravel- 

 beds may occur over the area which lies between 

 Poole and Dorchester, but whether such is the 

 case or not, I am disposed to consider the high-level 

 gravel east of Poole as an outlying mass of the 

 same age as that which caps all the tabular hills 

 of Devon and Dorset, as far as the valley of the Char; 

 and this, from the presence of these materials alone. 



* De Caumont, Topog. 

 t Trans. Geol. Soc. 2 ser. 



de Calvados, 

 vol. vi. p. 448. 

 X See Lyell, Trans. Geol. Soc. 2 ser. vol. ii. pi. 30, for a 

 section of part of this line. 



