1804.] MICROSCOPICAL JOURNAL. 173 



This belongs to the Eocene period before the Oligo- 

 Cene Tertiary. 



The California Infusorial stratum which was discovered 

 by Bailey at San Pablo, near San Francisco, and near by 

 which I lived nearly two years, and the Monterey and 

 Santa Monica, is Oligocene though ranked as Miocene by 

 most geologists. 



Cooke gives an analysis of the Drakesville, N. J., In- 

 fusorial stratum, which is as follows : 



Silica 80 60 



Alumina 8.84 



Lime 58 



Loss on ignition (orgauic matter and water)... 14.01 



99.09 



It belongs to the iceberg period. 



In Mexico, near Socorra, within 12 miles of the city is 

 a vast layer of Infusorial earth which is Eocene also. 

 It seems to belong to the Occidental Sea, but it has not 

 been investigated as yet. 



Now we sen that the Eocene does not contain any 

 alumina and is not a clay, strictly speaking. But the 

 iceberg period strata, both in Bohemia and in New 

 Jersey are clays made by the breaking down of the 

 granite. This is a difference between those from the 

 Eocene and iceberg strata, and it has been rendered solid 

 by the solution of the silica and not by the clay. 



I do not know of them except the Franzeubad, which 

 has been analyzed, and which is also known as Soos. 

 In contains too large a quanity of Campylodiscus. In 

 the Eocene of Utah lake and of Mono lake and of Pyra- 

 mid lake, there is present a Surirella utahensis of Ehren- 

 berg. But this is Surirella striatula of Turpin, 1828. 

 It is the Navicula (?) striatula of Ehrenberg, 1838, but 

 is a true Surirella. Surirella striatula is brackish and 

 marine. It is also fresh water in one " Keiselguhr von 

 Franzenbad." In fact, it sometimes occurs circular in- 

 stead of elongated, and looks as if it were passing into 



