4 A. M. EDWARDS ON FOSSIL DIATOMACE.E. 



cannot expect it to affect them now. And we must look foi 

 something into which they were developed if we believe in 

 evolution at all. The diatoms here are in small quantity mixed 

 with a high percentage of sand and clay, and in the white clay 

 only ; at least I have not been able to find them in the yellow. 



I detail the method used in searching for the diatoms, so 

 that observers may see that care has been exercised. Filtered 

 water was always used. The rock is broken in pieces and 

 washed with filtered aqua ammonias; this is nearly all poured 

 off, and finely powdered bichromate of potassium added in 

 excess. After a time sulphuric and a small quantity of hydro- 

 chloric acid is poured on and let stand for about a quarter of 

 an hour. The whole is washed until colourless, treated with 

 aqua ammonias, and again washed. A portion of the deposit is 

 dried on a slide, and a freshly-prepared solution of gum Thus 

 in wood spirit or alcohol added ; the slide is then warmed to 

 drive off the spirit, the cover glass imposed and pressed down. 



I do not see how foreign diatoms can be introduced in this 

 process unless by the acids, spirit, etc., used, but the forms are 

 always fresh-water ones, and the same solutions and acids have 

 been used to clean and mount marine Diatomacea3, and no fresh- 

 water forms have been detected amongst the latter. Moreover 

 the valves are often seen involved in the clay. Species identi- 

 fied are : — 



Cy rubella cistula, Hemp. Navicula elliptica, Ktz. 



Epithemia gihba, Ehr. „ viridis, Ktz. 



„ turgida, Ehr. Nitzschia scalaris, Ehr. 



Fragilaria striatula, Grev. Stauroneis plioenic enter on, Ehr. 



Melosira cremdata, Ktz. Synedra ulna, Ehr. 



Navicula dicephala, Ehr. Spicules of fresh-water sponge. 



I have submitted this material to the examination of a well- 

 known geologist, and he thinks the Diatomaceae may have been 

 washed in by percolation. I do not see, however, that this can 

 be the case, for the clay was hard and came from the interior 

 of the specimen. 



In conclusion I believe the loess was formed in the same way 

 as this, i.e., on large meadows, and not by the wind, in spite of 

 the opinion of Baron Von Richthofon to the contrary. The 

 loess of Germany, China, and America belongs to the Iceberg 

 period, 



