PROCEEDINGS OF THE SOCIETY. 549 



Dr. Millar said that what the Society had hitherto supplied that 

 they were supplying now. 



Mr. Shrubsole read a paper on " The Diatoms of the London 

 Clay" (seep. 381). 



The President inquired if Mr. Shrubsole had found the sulphide 

 of iron filling the interstices of the diatoms ? 



Mr. Shrubsole said he found it partly so in some instances and 

 entirely so in others ; it did not always replace the silica. 



Mr. Gr. D. Brown thought that the species of Triceratium referred 

 to were not the same as those now found in the Thames. 



The President said that those who studied this class of subjects 

 would be greatly interested in the paper which had been brought 

 before them. The London clay had at the bottom of it considerable 

 beds of pebbles, and they were all waterworn and were produced on 

 an old shore. Above this pebble bed on a sinking shore would be just 

 the place where they should expect to find diatoms. But the London 

 clay further above became a little more marine. Then it should be 

 remembered that the occiu'rence of diatoms was subject to great 

 variations, and they were always found on the sea floor in greatest 

 abundance in the neighbourhood of siliceous rocks or of their 

 wreckage. As regarded their age, he thought there could be no doubt 

 that they lived at the time of the lower Eocene. There were, however, 

 some special peculiarities about the London clay, there being no other 

 strata of the age which were known to have been deposited under the 

 same conditions. It was not a reef deposit or deep-sea deposit, but it 

 positively told the story of a sea, and an open estuary leading to a 

 very large river. This was one reason why they would not find the 



influence of unavoidable minute differences in the gauge-taps, while it would not, 

 in any degree, interfere with tlie fitting of tlie object-glasses. 



" It may, in conclusion, be remarked, that the plan last recommended by the 

 Microscopical Society has been found to work well amongst those who have 

 adopted it. their object-glasses being interchangeable ; and that several Micro- 

 scopes, to which the standard screw has been applied by the author of the paper, 

 have since been altered in other hands, so as to receive the proposed gauge-tap, 

 and consequently the object-glasses of all the principal makers ; and, further, that 

 the slightly increased looseness of fitting of their own object-glasses has not becu 

 found to occasion any practical iuiouvenience." 



See also the following appended to Proceedings of IGth June, 1858 :— - 

 " " Some difliculties liaving occurred in the practical application of Whitwortli's 

 gauges recently recommended by the Society for the purpose of establishing an 

 uniform screw for object-glasses, it was resolved at the meeting of the Society on 

 May 19, that ' Two dozen steel taps be made for the use of makers of Microscojies, 

 wishing to adopt the universal attachment for objeul-glasses recommended by the 

 Society.' 



" If one of these taps be made to enter the body of the Microscope it will 

 rtceive any oliject-glass having a screw of the dimensions recommended, and the 

 cylindrical gauges will not be required." (Quart. Journ. Micr. Sci., vi. (1S58) 

 p. 258.) 



Also Resolution of 30th March, 1859 :— 



" It was resolved, Tiiat the microscope-makers who adopt tlie standard screw 

 be requested to ascertain that one of the gauge-taps, recommended by the Society, 

 will enter the bodies of their Microscopes to the extent of three-tenths of an inch. 

 (Quart. Jouru. Micr. Sui., vii. (1859) p. 263.) 



