249 



GEOLOGICAL MANIPULATIONS. 



ON THE PREPARATION OE CLAYS, SANDS, AND CHALK, 

 EOR MICROSCOPICAL PURPOSES. 



By T. Rupert Joxes, Esq., E.G.S. 



To obtain microzoa from Gault, London, Speeton, Kimmeridge, Oxford, 

 Lias, and other clays, pieces of the clay, well dried in the sunshine or 

 in an oven, should be placed in a glazed pot or pipkin, and covered 

 ^vith boiliug-hot water. The clay will fall more or less completely into 

 a muddy mass, which must be worked up with the water by the hands 

 into a nearly uniform creamy consistence, and the thinner supernatant 

 fluid then poured off. This process will be completed only by several 

 repeated waterings, kneadings, and off-pourings ; together with occa- 

 sionally the drying of the undissolved portions of the cla}-, and again 

 subjecting them to the hot- water process and repeated manipulation, 

 until a small quantity only of sandy clay remains. Ihis, after having 

 been dried, should be boiled in water either in a flask over a lamp or 

 gas-light, or in a small saucepan on a nre for an hour or more, when, 

 the muddy water liaviug been poured away, the residue will be probably 

 sand, fragments of shells, and numerous small foraminifera, with 

 perhaps bryozoa and entomostraca. 



Some fossiliferous deposits, such as the Bracklesham sands and clays, 

 the Barton shelly clays, the Crag, the Calcaire Grossier of Paris, the 

 Falunian beds of Bordeaux, kc, fall readih'into a loose state in Avater, 

 sometimes even without much stirring. In this case, the supernatant 

 water should be poured through muslin or a fine sieve, that the small 

 foraminifera should not be lost. In clays, these minute shells are 

 generally tilled with the matrix ; but in sandy beds they often remain 

 empty, and therefore float in the water. The discoloured and muddy 

 water having been repeatedly poured ofl' from the washed sand (whether 

 the sand be siliceous or calcareous, in the latter case being probably the 

 detritus of shells or bryozoa), the residue should be dried, and then 

 sifted into various degrees of fineness for convenience of picking. 



Fig. 1. Fig. 2. Fig. 3. 



A, a, internal cylinder, witlif), b, in-tnmed rim ; c, perforated zinc plate or sieve ; d, d, half of per- 

 orated plate 0 ; e, e, outer cylinder ; /, /, in-turned rini. 



It is sometimes more convenient to sift the washed materials whilst in 

 the wet state, and to dry the several siftings in succession on a stove or 

 in an oven. In this case, a metallic sieve, constructed so as to allow of 

 the use of several moveable bottoms of perforated zinc, of difl'erent 



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