THE society's NOTE-BOOKS. 119 



at present the examination by far abler microscopists has given no 

 new forms, it has been a source of great interest to myself. 



The Foraminifera were obtained at a depth of about 23 feet, 

 and the section shows that except for a few inches of soil on the 

 top, it consists entirely of Silt, and it is to the nature of this Silt 

 (which is little known even to geologists or others out of this 

 neighbourhood), that I purpose directing your attention. 



Silt is very generally confounded with Sand^ and chemically 

 speaking they are very nearly the same, but in their physical pro- 

 perties Sand and Silt have but little resemblance. Sand, as is well 

 known, becomes firm and hard under a covering of water ; not so 

 Silt ; it flows nearly as readily as water itself. Sand is heavy and 

 sinks rapidly in water^ leaving it clean ; whilst Silt floats in running 

 water, and in still water it is deposited but slowly ; the water con- 

 tinuing turbid for a long time. 



Perhaps the readiest way to give a correct idea of its character 

 would be to state that it is a deposit, (from a state of suspension in 

 sea- water,) and that its component parts appear to be what may be 

 termed, from its extreme fineness, " powdered sand," with an ad- 

 mixture of loam, and an uncertain percentage of shells, chiefly 

 Foraminifera and Ostracoda, with a very small quantity of decayed 

 vegetable matter. It should be observed that the presence of 

 Foraminifera proves this Silt to be of marine origin, whereas Sand 

 is often of fresh-water origin. 



J. W. Measures. 



Dr. Measures kindly forwarded to me about four ounces of 

 this Silt for examination. I hastily "floated" the Silt to obtain 

 the Foraminifera from it, and found it contained many. 



The Silt is remarkably rich in species of Foraminifera as well 

 as of the Ostracoda. Although the quantity of shells obtained 

 from the four ounces of Silt is less than half a small teaspoonful, 

 yet from considerably less than a tenth part of this quantity I have 

 mounted a slide containing 48 species, from which I am induced 

 to suppose that if a quarter of a hundredweight of the Silt was 

 well dried and " floated," probably the number might be largely 

 increased — perhaps doubled. It would be needful to collect from 

 several localities a hundred yards or more apart. 



This Silt is the most difiicuU to " float " for Foraminifera, of 

 any similiar material I have yet had. There is something in it 

 which will not settle in the water until days have elapsed. At the 

 present moment, the water in which I floated my four ounces is 

 still thick and muddy, although three days since I did it. 



I B R A R Y 



