Tllli MODt;ilN EPOCH. 
353 
1 lie levels near Lewes, described in a former 
}>art of this volume, afford so interesting an illus- 
tration of the silting up of the disrupted valleys 
of the chalk, during a comparatively very recent 
jieriod, that we subjoin the following summary of 
the sequence of events which they record.* First, 
there was a salt-water estuary jieopled for many 
years by marine testacea identical with existing 
species, and into which some of the large cetacea, as 
the sea-unicorn, and porpoise, occasionally entered. 
Secondly, the inlet grew more shallow, and the 
water became brackish, or alternately salt and fresh, 
so that freshwater and marine shells were mingled 
in the blue argillaceous sediment at the bottom. 
Thirdly, the shoaling continued until the river 
water prevailed, and was no longer habitable by 
marine testacea, but fitted only for the abode of 
fluviatile species and aquatic insects. Fourthly, a 
peaty swamp or morass was formed, into which 
trees and terrestrial animals, as deer, were occa- 
sionally drifted by land-floods. Lastly, the soil, 
being only subject to periodical inundations from 
the river, became a verdant plain, through which 
the narrow Ouse now winds its way to the British 
contrary, is made up entirely of the chalk, proving that the valley 
coincides with a line of fault. The flinty chalk continues, with a slight 
southern declination, to near Southerham corner, where the lower chalk 
is again brought to view, and is seen tilted up in the chalk-pit near the 
turnpike-gate, and dipping at a considerable angle towards the north; 
the chalk-marl appearing beneath it. This section is a beautiful illus- 
tration, on a small scale, of the faults and dislocations pr oduced hy 
elevations and subsidences; and the Coomhe is a fine instance of a 
valley formed by the derangement of the strata. 
* I^rinciples of Geology, vol. ii. p. 27C. 
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