TRANSACTIONS OP THE SECTIONS. Gf 



lie works, such as quays, docks, basins, or breakwaters, intended to last for centuries, 

 the importance of considering whether limestone of any kind should be employed in 

 such structures below the ordinary level of low water at spring tides. 



Notice of Sections of the Railwaij between Bristol and Bath, a distance of 

 twelve miles, prepared by direction of a Committee of the British Associa- 

 tion. By William Sanders, F.G.S. 



The first was in length thirty-six feet, being at the rate of three feet to the mile. 

 The others were enlarged sections of four portions of the railway, made on the scale 

 of forty feet to one inch. One of these represented a cutting one mile in length 

 at Saltfovd, through the successive strata of the lias formation. This cutting was 

 described by detailed sections on the scale of four feet to the inch ; each bed is 

 noticed with, as far as possible, its included organic remains. The subdivisions 

 are, the upper marl upon upper and lower blue limestones fifty-eight feet, ivhite 

 limestones twenty-four feet, and lower marl twenty-seven feet ; which latter were 

 shown, by means of sinking a pit, to rest upon new red marls. Drawings of certain 

 fossils were added. Three other enlarged views of the Pennant strata were given, 

 with further details, in sections on a scale varying from twenty to ten feet to the inch. 

 Drift beds were noticed containing water-worn fragments of sandstone, broken stems 

 of plants {Sigillaria and Lepidodendron), with rolled pieces of perfectly formed coal; 

 also conglomerates of broken coal. Drawings were made of two large Sigillaria taking 

 origin in a bed of coal; and a portion of two large slabs of the Pennant sandstone, 

 showing very regular ripple-marks. Various other geological phEenomena deemed 

 worthy of attention were displayed on the sections. 



Notice of Sections of the Railways between Glasgow and Greenock, and 

 Greenock and Ayr, prepared by direction of a Committee of the British 

 Association. By John Craig. 



A Letter was read from T. B. Jordan, of the Museum of Economic GeO' 

 logy, ' On Copying Fossils by a Galvanic Deposit.' 



In applying the method ordinarily used in electrotyping, some difficulty v^^as expe- 

 rienced by the author in consequence of the irregular form of the fossils, parts of 

 which would not relieve from the wax or plaster matrix in which the copper is after .» 

 wards deposited. Mr. Jordan therefore adopted a compound of glue and treacle (used 

 by printers for their inking-rollers) as the material of the moulds, the elasticity of 

 which admitted of its leaving the adherent portions without breaking. The mixture 

 is applied hot, and allowed to harden for twenty-four hours, when it will come oiF 

 without injuring the finest parts. The matrix thus prepared requires a strong varnish 

 to protect the back and sides from the action of the liquid in which it is to be placed, 

 and only one copy can be made from each matrix ; but the impressions have none of 

 the defects so apparent in those produced in the ordinary moulds. Different lights 

 and shades may be given to the copper impressions by a galvanic process, which the 

 author considers capable of improvement and application to other purposes. For a 

 dark object on a light ground the surface is brushed over with the argento-cyanide 

 of potassium, giving it a silver face, which may be removed to the desired extent from 

 the portions requiring to be dark, by a dilute solution of nitro-muriate of platina. 

 Other tints may be produced by using a solution of gold ; and all may be consider- 

 ably varied by changing the time during which each solution is allowed to act. — 

 [Specimens of the electrotype copies of Trilobites and other fossils were exhibited.] 



Notice of Models for Illustration of the Succession and Dislocations of Strata, 

 Mineral Veins, ^c, constructed by T. Sopwith, F.G.S. By the Rev. Dr. 



BUCKLAND. 



Major S. Gierke called attention to the ' Atlas of Sieges and Battles in the Peninsula,' 

 published by Mr. Wylde, and constructed from original sketches taken under the di- 

 rection of Sir George Murray, by Sir Thomas Mitchell, now Surveyor-general of New 



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