70 MICROSCOPICAL OBJECTS FOUND 



atoms of lime, along with some sand. This is a 

 very singular and Chalk-like rock, but my speci- 

 cimen contains no trace of microscopic organi- 

 zation. 



A pure white specimen of the Estuarian marl 

 of the Pampas,* exhibited very similar results, 

 with the exception of a few delicate white 

 threads resembling very small branching corals. 

 I have not, however, been able to satisfy myself 

 of their organic nature. 



A brown coloured specimen from the same 

 deposit contained a much larger amount of sand 

 and silt. The lime was apparently diffused 

 through the whole, and under the microscope was 

 undistinguishable from the mud. 



A green siliceous rock from New Jersey, very 

 like our English lower green sand, (sent me by 

 Professor Ansted,) in which the shells still retained 

 their calcareous organization, exhibited large 

 rounded grains, of very dark green sand. 

 Amongst them were a few Foraminifera, and in 

 some specimens numerous detached shell prisms, 



"^ See Darwiu's Journal, p. 149. First Edition, 



