202 



On a Diatomaceous Earth from Guatemala, and the Occur- 

 rence OP Marine Diatoms in Fresh Water. 



By Arthur M. Edwards, M.D., Newark, N.J., U.S.A. 



(Read January 20th, 1893.) 



Having received from Mr. G. C. Karop a sample of earth 

 labelled " Diatomite, Guatemala,"* I wisli to report on it at 

 this time, more especially as it gives me an opportunity of 

 making known the results I have arrived at insstudying the 

 Diatomacese in connection with the subject of the occurrence of 

 marine forms in fresh water. 



This brings me to speak of the origin of Diatomacea3, whether 

 fresh water, brackish water, or salt water or marine. The 

 Guatemala earth is a white powder, and, although the geology 

 of it has not been studied, or at least has not been communi- 

 cated to me,t I should judge from the examination of it micro- 

 scopically that it is an example of which we have many in the 

 northern United States or Champlain area, that is to say, 

 deposits which have been thrown down during the post-glacial 

 or iceberg period, when the ice formed in the glacial period 

 was melting, and warmer weather succeeded, and a fi^esh water 

 sea, with DiatomaceJB, lived and died, their siliceous shells 

 being deposited on the bottom. I judge this to be the case by 

 comparison of it microscopically with those deposits with which 

 I am familiar in Canada, the United States, Germany, Great 

 Britain, Italy, and Sweden. It is purely siliceous,;}: and con- 

 sists of the following forms : — 



Amphora ovalis, Ktz. Melosira undulata, Ktz. 



Biddulphia Icevis, Ehr. Navicula afflnis, Ehr. 



Cocconeis lineata, Ehr. „ hacillum, Ehr. 



„ placentula, Ehr. „ cryptocephala^'Ehr. 



* Obtained from Mr. A. Ashe. 



f Mr. Ashe informs me that inquiry has been made on this point but 

 without result. — Ed. " Q. M. C. Juuru.'' 

 X See Aualysis at end by Mr Ashe. 



