1894 THE MICROSCOPE. 117 



process of cleaning is the same as that already described. 

 The salt in the salt water only necessitates the using of 

 a smaller quantity of hydrochloric acid. 



When gatherings are made containing fine sand, as is 

 commonly the case, it is rather difficult to concentrate 

 them and separate the bacillarian shells from the sand, 

 and in all cases we must expect to loose some of the 

 bacillariacese. But I do not now intend to go into this 

 branch of the subject. 



Fossil deposits of bacillariacese are always made up of 

 matter which contains clay in more or less quantity, and 

 this modifies the mode of procedure in cleaning them in 

 such a way that the shells may be eliminated, mounted 

 and shown. 



To begin with those containing a small amount of 

 clay pulverulent and easily cleaned. The fresh water 

 clay from Bowkerville, N. H., also known as Keene, N. 

 H., is an example. This can be readily cleaned. It is 

 only necessary first to boil it in weak aqua ammonia, add 

 pulverized bichromatic of potash in excess, add oil of 

 vitriol and hydrochloric acid. Clean with filtered water 

 and add weak aqua ammonia and clean in filtered wa- 

 ter. Next keep it in water to which salicylic acid or oil 

 of cinnamon is added. In fact such a deposit is cleaned 

 very much in the same manner as recent gatherings, 

 the clay being removed by aqua ammonia, in which it is 

 soluble. Sand is not present so that elutriation is un- 

 necessary. 



Next we have to deal with deposits like the fresh wa- 

 ter indurated clay found near Virginia City, Nev., and 

 which is known in commerce as electo-silicon. This is 

 more difficult to clean, mainly on account of the large 

 amount of clay present and the indurated character of 

 it. This induration led me, at a former time, to class 

 deposits of this character as volcanic being supposed to 

 be formed in volcanic districts, and therefore as sub- 



