Subsurface Laboratory Methods 103 



during the Miocene. Following Miocene time they decreased rapidly but 

 were still present in large numbers. It is impossible to predict how much 

 diatomaceous ooze is now being deposited on the present ocean floor. 



Marine diatoms flourish in all latitudes and at all seasons of the year, in 

 the warmer and coldest seas. It is well known that they are so abundant in 

 frigid zones as sometimes to colour the seas and to tinge with a particular 

 hue the blocks of floating ice. 



They are capable of surviving in conditions so diverse, it is difficult to 

 believe that any fixed laws of geographical distribution can be discovered 

 with respect to them; on the contrary, it might be supposed that the con- 

 tinuity of adjacent seas, the surface and submarine currents, the movement 

 of tidal waves, the existence of periodical and other winds, the traffic of 

 ships and the movement of fishes would all tend to facilitate or bring about 

 the mingling of local floras. ^^ 



Diatoms offer great possibilities for establishing local and world- 

 wide correlations because of their pelagic character and the siliceous 

 nature of their skeletons. Attempts have been made in California and in the 

 Netherlands East Indies (Java) to use diatoms for subdividing certain 

 parts of the Tertiary sequence. 



Cleaning the diatoms out of different samples is a tedious business. To 

 clean a sample of a fossil marl thoroughly, when the particles are solidly 

 cemented together perhaps with some volcanic material enclosing the fragile 

 microfossils, is not a small task and requires even from the most experienced 

 cleaner much skill and patience. Different chemical agents may be used, 

 depending on the chemical character of the matrix; too strong solvents may 

 destroy the diatoms entirely, which happens sometimes in the most unex- 

 pected manner, as any diatomist knows. After the texture of the rock has 

 been loosened and something like a dispersion has been obtained, the ma- 

 terial may be sifted through very fine sieves, 150- and 300-mesh, and sub- 

 jected to several washing operations, decanting after a fixed time. The well- 

 known sulphuric-acid treatment with either potassium chlorate or nitrate for 

 bleaching is in almost any case inevitable. The whole process cannot be hur- 

 ried through and must take its time. It may last several weeks. However cum- 

 l ersome the process of cleaning may be, well-cleaned samples are extremely 

 important and save much time in the inspection and sorting. Only in the 

 case of well-cleaned samples, a complete review of the fossil content is 

 possible and the diatoms accessible to further study and to be photographed 

 and arranged in neatly mounted slides, which allow a close and thorough 

 inspection. Fragments have as a rule to be disregarded except in instances 

 where a view of the internal structure is wanted. When incomplete tests are 

 inspected, errors will heap up, for studying rare and unknown diatoms from 

 badly conserved and imperfectly cleaned fragments leads to false determina- 

 tions, which may remain undetected in case of a study purely in search of 

 new and strange forms, but when the establishment of fossil lists for strati- 

 graphic use is planned, wrong determinations may seriously influence the 

 result as to the zonal distribution of the fossils and the geologic age of the 

 samples.^'* 



^' Castracane, Fr. D. A., Report on the Scientific Results oj the Voyage of H.M.S. Challenger Dur- 

 ing the Years 1773-76: Botany, vol. 2, p. 9, 1886. 



■"^ Reinhold, Th., Fossil Diatoms of the Neogene of lava and Their Zonal Distribution: Geol.-mijnb. 

 genootsch. Nederland en Kolonien Verh., Gaol. ser. Deal 12, pp. 43-133, 21 pis., 1937. 



