AUSTEN — TERTIARY DEPOSITS OF THE SUSSEX COAST. 



65 



outer edge. This state has been a permanent one, as part of this 

 shingle has become overgrown by trees and bushes. On the land- 

 side is a line of vertical cliffs which the sea never now reaches, but 

 which belonged to the period of the accumulation of the shingle at 

 its base, and when the whole was placed at a lower level ; so that 

 here again is an indication of a rise. 



Like proofs of the elevation of a former line of coast-shingle may 

 be seen on the opposite side of the entrance into the Southampton 

 Water, as in the parish of Alverston round from Gomer to Anglesey. 



2. Portsmouth Harbour. — In 1847, Capt. (now Col.) H. James, 

 R.E., described a section which was exposed in excavating the new 

 steam-dock in Portsmouth Harbour '•'. Beneath an upper bed of 



Fig. 5. — Section at Portsmouth Harbour. 



___ High-water-line. 



1. Mud of the present Estuary 1 



Low-water-line. 



2. Sand and shingle 2 



3. Estuary mud with shells : 4 f. 3 



4. Mud and vegetable matter : 2 ft. ..4 



5. Stumps of trees h 



6. Loadon Clay 6 



mud (fig. 5, i), such as now covers the whole of the Portsmouth 

 Harbour area, was a bed of flint- shingle ; the level of this was about 

 2 feet under the lowest ebbs : beneath this was a deposit of blue 

 mud, with the usual estuary shells ; and lastly, a band containing 

 much vegetable matter. In this last, the common Grass-wrack 

 {Zostera marina) was recognized, together with Truncatella Mon- 

 taguei. There were also the prostrate stems of trees, and stems 

 rooted in the subjacent London clay. The inferences to be drawn 

 from Capt. James's observations are as follow : — 



This section shows a former terrestrial surface at 8 feet and more 

 under the level of low-water (from 16^ to 29 feet below high-water), 

 and which passes with a slight dip to a greater depth still beneath 

 the adjacent portion of the harbour. The original terrestrial surface 

 must necessarily have been above the high-water level, — or the vertical 

 depression here indicated must be estimated at from 40 to .50 feet at 

 the very least. The band with Zostera and Truncatellcp. shows 

 that the depression was gradual, and that the Portsmoutli Creek 

 at that spot was then more brackish than it is now. 



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

 VOL. XIII. PART I. F 



