Document 35, p 11
| These Bridges the first being in part, and the latter wholly upon Gravel | ||||
| of unfathomable depth, were founded on bearing Piles encased with Sheet | ||||
| or plank Piles, below the Bed of the River, the space being filled up, and | ||||
| the foundations further defended by the deposition of tough Quarry rubble | ||||
| Stones; and Mr Smeaton having experienced the great dependence, and | ||||
| power of resistance of Stones SO deposited, not only in Cases of Building the Bridges | ||||
| above mentioned, but in a very great variety of Cases, preceeding those under- | ||||
| -takings as well as after wherein he found them the most effectual means, | ||||
| not only of controuling the violence of rapid Rivers but of the Sea itself; he was | ||||
| naturally led to place very great Confidence in that species of defence. | ||||
| 4thly that partly from the report of Mr Pickernel's borings, partly from the | ||||
| Similarity of the situation of the place proposed by Mr Errington to that where | ||||
| Sir Walter Blackett and Mr Wooler had worked; being both of them near the | ||||
| bottom of an extensive pool wherein the Water is kept up by a Bed of Gravel | ||||
| just below them and forming as it were a natural Dam, whereby the motion | ||||
| of the Water in the Pool above, in the low states of the River, was scarcely | ||||
| perceptible; I say from similarity of situations, Mr Pickernel's report of | ||||
| the Ground just above the place pitched upon by Mr Smeaton, and the | ||||
| trials that he (Mr Smeaton) made himself (by driving a sharpened Iron | ||||
| Barr from 9 or 10 feet into the Bed of the River in several places which was | ||||
| very consbly less resisted and particularly in the Main Current, after | ||||
| it was driven down some feet, than it was in entering the upper Crust of | ||||
| the Gravel Bed, which was apparent to him by his assisting personally in the | ||||
| operation) from all these considerations he thought himself well justified in | ||||
| concluding that at some depth exceeding 9 or 10 feet, at this place, that there either | ||||
| actually existed a Stratum of Quicksand, similar to that at the west end of | ||||
| Tyne Green, or at least matter so little compact or capable of bearing weight, | ||||
| that to drive Piles into it would only weaken the Stratum. The question | ||||
| therefore that he had to decide for his own guidance, was whether there was a | ||||
| Bed of Gravel of a sufficient thickness and compactnessto bear the Weight of a | ||||
| Bridge in case it was unwounded and unbroke: and the experiment of the | ||||
| 11 Barr | ||||
Note: Mr Smeaton's Memorial concerning Hexham Bridge, p 11
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Transcribed by CTW and KS