VOL. XXVII.] PHILOSOPHICAL TRANSACTIONS. 683 



for extraordinary inundations of the Thames, there is at this day a mark, which 

 if occasioned by an inundation, must have been that of a prodigious one, be- 

 yond any ever known to have happened in that river ; which is a bed of shells, 

 if not of a kind of marble too, lying across the highway on the descent near 

 Stiffbrd-bridge, going from S. Okendon. Below this bed of shells, at above 

 50 or Go yards distance, in the bottom of the valley, runs a brook, that empties 

 itself into the Thames at Purfieet, about 3 miles from thence ; which brook 

 ebbs and flows with the Thames, but not at any certain height, by reason of 

 mills standing on it ; but above a pretty high- water in the brook, the surface of 

 the bed of shells lies above '20 feet perpendicular. Consequently if this bed of 

 shells was reposited in that place by an inundation of the Thames, it must be 

 such as would have drowned a vast deal of the adjacent country, and have over- 

 topped the trees near the river, in West-Thorrock, Dagenham, and the other 

 marshes, and probably by that means over-turn them. 



For had these trees been left there by that deluge, we should not find the 

 bed of earth, in which they grew, so entire and undisturbed, as it manifestly is 

 at this day, a spongy, light, oozy soil, full of reed-roots, and of much less 

 specific gravity than the stratum above it. Whereas I can from experiments 

 affirm that in three places where I have tried it, the strata are in a surprising 

 manner, gradually specifically heavier and heavier, the lower and lower they lie. 



As to the manner how these trees came to be interred, I take.it to be from 

 the gradual increase of the mud, or sediment, which every tide of the Thames 

 left behind it. I presume those trees might be thrown down before the walls or 

 banks were made, that now keep the Thames out of the marshes ; and then 

 they were covered every tide. And as they lay thick, and near each other on 

 the ground, they would soon gather a great deal of the sediment, and be soon 

 covered with it. And after the Thames-walls were made, every breach in them, 

 and inundation, would leave great quantities of sediment beiiind it ; as I by a 

 troublesome experiment found, in going over some of the marshes, soon after 

 the late breach, where I found the mud, generally above my shoes, and in many 

 places above my knees. And it is a practice among us, of which we have divers 

 instances, that where a breach would cost more to stop, than the lands over- 

 flown will countervail, there to leave the lands to the mercy of the Thames; 

 which by gradually growing higher and higher, by the additions of sediment, 

 will in time shut out the water of the river, all except the highest tides. And 

 these lands they call saltings, when covered with grass ; or else they become 

 reed-grounds, &c. 



That it was the sediment of the Thames, that buried those trees, is further 



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