77 

 fresh water as can be obtained for cleaning. Thereafter it is moun- 

 ted, as it is called, in gum thus, which is the material I always use 

 for mounting microscopie objects, and it is examined. It is found to 

 be made up of the shells of Foramenifera, Radiolaria, Bacillaria and 

 Sponge spicules, as are the deposits of marine Diatoms, as they are 

 called, everywhere. But it is also found to have an almost transpa- 

 rent brownish colored substance, almost of the color of burnt sienna, 

 as painters cali it, diffused through it. This is asphaltum which has 

 not been acted on by the alkali used in cleaning. It can be volatil- 

 ized by heat, so that the earth can thus be rendered colorless or 

 nearly so. Now although the asphaltum occurs disseminateci throu- 

 ghout the mass it is also found within the shells of the Forameni- 

 fera and Bacillaria, so that the lorica, as they are called of the Ba- 

 cillaria are opaque or colored of a reddish brown. 



And often when the Diatom is made up of the entire shell or 

 when the frustule, as it is called, has the valves united, as is common 

 in Coscinodiscus, which is frequent, and is seen to be present in a 

 form that is rounded or as spheres, the asphaltum is present, showing 

 that it is present, showing that it was fluid or vapourous when in- 

 troduced and becomes hardened afterwards. Showing that it first 

 means petroleum or rock oil and asphaltum at last by evaporating. 



The stratum which contains Bacillaria at Santa Cruz, California 

 is likewise worked but it is poor in asphaltum but rich in Diatoms. 

 Over it is a dark layer which is interesting and which I obtained 

 from there. This does not contain any Diatoms at ali, but that it 

 has formed in shallow water most likely. A layer of mud, such as is 

 common now ali along the coast it contains something that makes 

 it dark in color but it is not asphaltum. In fact I had similar layer 

 from near San Francisco. 



Where the stratum contains shells of Bacillaria and is pronoun- 

 ced Eocene by geologists and constitutes the London clay from Lon- 

 don in England, and which Schrubsole found to be Diatomaceous, 

 is examined microscopically it found that the Diatoms are scarce in 

 it. They are marine Diatoms markedly, but the organic matter, which 

 was endochrome, is removed or changed and replaced by carbona- 

 ceous matter which is also present in rounded masses and black by 

 transmitted light. Sometimes it is replaced by pyrites or sulphide of 



