PROF. W. r. WILrJAMRON ON MINERALIZATION. 193 



specimen of the animal of a species of Rotalia from the West 

 Indies, which has drawn in all its threads and tentacles 

 within its chambered house. Take a flint of the Chalk, so 

 common in this part of the world, and with a convenient 

 little hammer chip off the thinnest and smallest flakes of 

 this flint — the thinner they are the better — put them first 

 into turpentine and then successively under the microscope. 

 Persevering in this research, you will accumulate a collec- 

 tion of minute silicified organisms, including Foraminiferous 

 animals, some within and others deprived of their shells. 1 

 have on the table such microscopic animal preparations in both 

 these conditions. But I have also on the table a specimen, for 

 which I was indebted, a long time ago, to my old friend and 

 fellow-worker — when we were together investigating the Fora- 

 minifera — I mean the late Dr. W. B. Carpenter. It is a specimen 

 demonstrating the existence in the ^gean Sea of what you are 

 all familiar with under the name of " Foraminiferous ooze," but 

 in this particular specimen all the calcareous elements of the 

 ooze are eliminated; but though the shells have gone, the 

 animals are preserved in a silicified state — not imbedded in 

 Silex, but the animals have shown their affinity for Silica by 

 allowing their protoplasm to be replaced by that substance. 

 Just fancy an Amgeba capable of being silicified ! There would 

 apparently be no difficulty about the silicification of the Amaeba 

 if put under favourable circumstances, because it is not more 

 highly-organized than these Foraminifera are. Here we have 

 a demonstration of the close affinity that Silica and animal sub- 

 stances have for one another. But in addition to the above 

 states, we further find in these flints other Foraminifera, in 

 which not only the protoplasmic animal, but also the calcareous 

 shell is replaced by Silica. 



On turning our attention to the larger fossils found in the 

 Chalk, we shall discover that the same affinity of Silica for organic 

 matter is shown in a large number of them. Thus, in many of 

 the Echini that you get from the Chalk, such as the genus 

 Spatangus, etc., their shells still retain their normal Carbonate 

 of lime, but the animal in the interior has disappeared and been 

 entirely replaced by Silica. 



One more example of mineral replacement may be quoted, in 

 which iron is the replacing material. This is seen most 



