84 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [DoC. 21, 



Fountain Lake. It rests everywhere directly on the Eocene sands 

 and clays ; and its lower beds are in a great measure made up of 

 these underlying sands and clays re-deposited. This is so much the 

 case, that it is often difficult, even in the open cuttings, to distin- 

 guish between the top of the Eocene and the bottom of the mud. 



Change of level, or possibly the silting up of some narrow inlet 

 to the tidal water, must at some time have converted this mud- 

 deposit (A) into a land-surface, as its surface, where not eroded, is 

 seen dotted over with the stumps of trees of small growth — possi- 

 bly Alder or Willow, their roots often penetrating downwards 

 vertically to the depth of 5 feet. The present surface of this root- 

 bed stands at from 3 feet above to 2 feet beneath the present low- 

 water level of the harbour. It is this root-bed, probably, which 

 has been described by Sir Henry James * as occurring beneath the 

 dockyard at a depth of from 4 to 14 feet beneath low water. 



I do not see exactly in what way to account for the difference 

 of level of the root-bed shown in the Mud-section and again 

 beneath the dockyard, except by supposing a subsidence of the 

 underlying Tertiary deposits. It is at least worthy of notice that 

 the dip of the root-bed in this area corresponds in direction with the 

 dip of the Eocene strata on which it rests. 



The mud-bed B, or recent mud-bed as it might be called, as com- 

 pared with the root-bed, commences at the foot of the low escarp- 

 ment, and, spreading northwards and westwards, rests everywhere 

 directly on the Eocene, or on the mud-bed A where this is present. 

 The surface of the mud (B) stands at from 6 to 7 feet above low- 

 water level, or just midway between ordinary high and low water. 

 One may suppose, indeed, other conditions remaining the same, 

 that this level would be indefinitely maintained, the flow, and con- 

 sequently the carrying powers of the water on and off the mud 

 being equal. A study of the sections tends to confirm this idea ; 

 for there is evidence in these of very slow deposition near the sur- 

 face of the mud in most places, and of very rapid deposition in a 

 few others — the rapid deposition, as along the edge of Fountain 

 Lake, being clearly the result of silting up to a certain level. 



The spread or overlap of the mud-bed B so far beyond that of A 

 seems to point to a cutting back of the gravel-capped escarpment, 

 for the same distance, since the submersion of the root-bed. 

 The gravel-bed iv contains no fossils. 



The root-bed contains rarely a few specimens of Littorina. 

 The mud-bed A is crowded with recent shells at and near the 

 surface, and usually also near its base. Antlers of the Eed and 

 Fallow Deer have also been met with in this bed. 



Thin beds of fine subangular shingle are seen in places, either 

 interstratified in the mud or near its base, and in all cases include 

 recent shells. 



It has been my good fortune while studying the above sections to 

 enjoy the friendship of several of the gentlemen in command of the 

 works; and to their assistance I am indebted for much valuable 

 * Quart. Journ. Geol. Soc. vol. iii. p. 249. 



