416 Notices of Memoirs — Francesco Castracane 



In spite, however, of this successful result, obtained by the most scru- 

 pulous attention and caution, to avoid the smallest possibility of 

 mistake, I confess that (from perhaps excessive timidity) I hesitated to 

 submit it to public opinion. I therefore resolved to await the result of a 

 contra-proof which I should be able to have by trying again a small 

 remaining piece of the same coal, not omitting to employ on each 

 occasion a perfectly clean test-tube that had never been used before. 

 I need not say what was my gratification at seeing some Diatoms again 

 in the field of the microscope ; thus confirming the correctness of 

 my previous experiment. And as a final argument I will add that 

 the forms I recognized and ascertained in the second experiment were 

 either more or less identical with those of the first, so that there 

 could not remain the least doubt of the presence of the Diatoms in 

 that coal. Hence it stood proved upon evidence that they must have 

 existed contemporaneously with the plants, the remains of which 

 serve as fuel in furnaces, and give life and motion to the countless 

 steam-engines which make distances vanish and promote commerce. 

 The Diatoms that I met with in this coal chiefly belong to fresh- 

 water genera and species, if we except perhaps a Grammatophora, 

 a little Coscinodiscus, and perhaps an Amphipleura, which appeared 

 to me to be the A. Banica. Amongst fresh-water Diatoms I have 

 distinguished the following : — 



Fragilaria Harrisonii, Sm. = Dontidium Harrisonii. 



Ephithemia gibba, Ehrbg. , Prz. 



Sphenella glacialis, Prz. 



Gomphonema capitatum, Ehrbg. 



Nitzschia curvula, Prz. 



Cymbella scortica, Sm. 



Synedra vitrea, Prz. 



Diatoma vulgar e, Bory. 



The influence of the sea, which is shown in the different shapes of 

 salt-water Diatoms (although only single specimens presented them- 

 selves among the many fresh- water ones in the residue of the Liverpool 

 coal), offers us an indubitable proof that the waters of the sea must 

 have penetrated amidst the remains of that ancient vegetation. 



To account for the presence of those few little marine forms among 

 fresh- water Diatoms, I do not think we can admit the hypothesis that 

 they were merely adventitious, as if carried thither by the wind. 

 Although there can be no reluctance to acknowledge that such a 

 transportation could take place, yet I do not find it possible to persuade 

 myself that some valves of marine Diatoms which have been now 

 and then detected in the atmospheric dust, may be precisely en- 

 countered amongst a small number of fresh-water Diatoms. It is to 

 be added, moreover, that I do not remember ever having met with 

 a notice of marine Diatoms being found in the atmospheric dust, 

 whereas fresh-water forms are often spoken of. 



It is truly an easy thing to understand how at the drying up of a 

 pond the wind may sweep away from the surface the minute siliceous 

 skeletons of Diatoms which have been growing there for generations ; 

 but one could not so readily understand how the same could happen 

 to those of the sea. However, the fact that at the very remote period 



