256 Mr. Pennlston on the Induration of Chalk. 



The immediate effect of this operation was more surprising 

 than the former : as the carts were backed into the river, and 

 their contents tipped into the stream, the consolidation was 

 almost immediate, for as the carts successively came with their 

 loads, the parts which had been previously filled in were ca- 

 pable of bearing the wheels, with their loads on them. The 

 whole wash was filled in at a comparatively slight expense, 

 and remains perfect to this hour. 



From these proofs it has occurred to me, that if the same 

 material were used to strengthen the bed of the Thames in the 

 line of the Tunnel yet to be excavated, it might be attended 

 with the happiest results. All that would be required, would 

 be to bring in barges a sufficient quantity of chalk earth, and 

 throw it into the river at low water : the current would do the 

 remainder of the work ; nor have I a doubt, if it proved 

 necessary to cut through a portion of this new-made bed in 

 some future excavation, that it might be done with as much 

 security as cutting through a solid rock of chalk. 



Having the honour of being acquainted with Mr, Timothy 

 Bramah, I have mentioned to him the result of the experi- 

 ments I have here described, and my opinion of their applica- 

 bility, if the Tunnel should be renewed. The trial would not 

 be a very expensive one, and I should be too happy if any 

 suggestion of mine could, in the slightest degree, be beneficial 

 in forwarding a work so nationally desirable to be completed. 

 I am, dear Sir, &c. &c. 



July 16, 1831. J. PENNISTON. 



FURTHER OBSERVATIONS UPON SILICEOUS DEPOSITS 



FROM THE URINE. 

 By ROBERT VENABLES, M. B., 



Physician to the Chelmsford Provident Society, &c. &c. 



HPHE existence of silex in the urine has been generally 

 admitted, upon the authority of Berzelius, and he believes 

 that it is accidentally derived from the water which we drink. 

 Silex has been found, in three instances, intermixed with the 

 composition of urinary calculi ; in two by Fourcroy and 



