Archive image from page 198 of Discovery reports (1934) Discovery reports discoveryreports09inst Year: 1934 MARINE DEPOSITS OF PATAGONIA 181 Fig. 2. Sieves stacked one above the other. a, rubber ring; b, sieve plate. sieves from above while they were vigorously shaken. The material was thus quickly sorted into its components of various diameters down to 0-5 mm. in diameter, and at the same time it was thoroughly washed free from salt. The material finer than 0-5 mm. in diameter passed through the finest sieve at the bottom of the stack and was discarded. The sieves were then separated, an
Archive image from page 198 of Discovery reports (1934) Discovery reports discoveryreports09inst Year: 1934 MARINE DEPOSITS OF PATAGONIA 181 Fig. 2. Sieves stacked one above the other. a, rubber ring; b, sieve plate. sieves from above while they were vigorously shaken. The material was thus quickly sorted into its components of various diameters down to 0-5 mm. in diameter, and at the same time it was thoroughly washed free from salt. The material finer than 0-5 mm. in diameter passed through the finest sieve at the bottom of the stack and was discarded. The sieves were then separated, and their contents dried and weighed. The figures obtained, in conjunction with those obtained from the levigator, were combined to show the percentage of the grades in the total sample. FINER MATERIALS A portion of the untreated sample was placed in a sieve with holes 0-5 mm. in diameter. This was then thoroughly agitated in a vessel of water so that all the material finer than 0-5 mm. in diameter passed through into the vessel, and the coarser material of all grades over 0-5 mm. in diameter remained in the sieve. The latter material was then well washed by a stream of water over the vessel, dried and weighed. The finer material that passed through the sieve was then levigated and thus separated into the two finest grades as described below. Borley (1923) found that in North Sea deposits the separation of grades VIII (fine sand) and IX (silt) could not be readily effected by decantation and so made use of a levigator. The method of levigation was adopted in this investigation as being more accurate and reliable than other methods. Schone (quoted by Borley) estimated that a vertical cur- rent of water travelling at 7 mm. per second would separate spherical quartz particles over o-i mm. in diameter from those under o-i mm. in diameter. Levigation by a vertical current of this speed was found by Borley to give a very good degree of accuracy (5 per cent) with North Sea deposits, and
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