The Diatoms of the London Clay. By W. H. Shruhsole. 383 



also, after some failures owing to hard frost, I found diatoms of the 

 same species, in the same condition, and at the same geological level 

 as at Heme Bay and Sheerness. I went next to the Loam Pit brick- 

 yard at Lewisham, and was rewarded with equal success. At this 

 place I learned from the workmen that when digging out the clay 

 they frequently observed " shining spots " in it. 



Gruided by the valuable ' Memoir of the London Basin,' Part 1, 

 by W. Whitaker, Esq., F.G.S., I visited several other localities. In 

 several cases I found that the sections accurately described ten years 

 before, were overgrown, or that the sites where such had been 

 were then built upon. On going to Bishoj)'s Stortford, however, 

 on the same errand, I gathered information which convinced me 

 that the diatoms are to be found in well sections in that locality. 



Interviews with Messrs. Docwra and Sons, Messrs. Le Grand 

 and Sutcliff, Mr. T. Tilley, and other prominent well-sinkers, who 

 very kindly gave me all the assistance in their power, put me in 

 possession of the knowledge that all round London, and indeed 

 almost anywhere in the London basin, clay appearing as if it had 

 been dusted with powdered sulphur, and sparkhng in sunlight, had 

 long been noticed whenever wells had been sunk within the indi- 

 cated area. 



In a well in progress at Prittlewell for increasing the water 

 supply of Southend, no diatoms were found until the depth of 360 

 feet from the surface (equal to 260 feet below Ordnance datam) 

 was reached. Much of the clay taken out down to 366 feet from 

 the surface was very rich. 



Dr. Bossey was the first to discover that besides the solid, heavy 

 forms, there were some that had not been so completely mineralized, 

 and would bear examination with high powers by transmitted light ; 

 and to guide others in separating these transparent forms, Dr. 

 Bossey has kindly given the following directions : — "Dry the clay, 

 and put it into a tall glass jar half full of water. Shake it gently, 

 let it stand three or four minutes, and then pour off the thin 

 portion. Piepeat this process as long as a turbid milky fluid can 

 be poured ofi". In thus washing away the lighter matter, always 

 leave an inch or two of water above the sediment. When the 

 sediment has been well washed, pour some fresh water into the jar, 

 and very quickly pour off the turbid fluid, leaving only coarse sand, 

 lumps of clay, &c. Eepeat this process three or four times, and 

 collect all that has been washed over, and set it aside till everything 

 has subsided from it. Pour ofi' nearly all the water from this sedi- 

 ment (which contains the diatoms), and put the sediment with a 

 httle water into a watch-glass. Blow air through a pipette into the 

 watch-glass, so as to set the whole of the contents whirling round 

 the watch-glass. While the fiuid is still in motion, put the point 

 of the pipette into the cone of floating matter which will be found 



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