26 GEOLOGICAL MEMOIRS. 



tions of plants, or calcareous polythalamia ; 5th, the greater number 

 of the ninety species already found equally occur in the most widely 

 separated of the places just named; 6th, the most numerous forms 

 are everywhere land and freshwater productions ; yet some marine 

 animalcules are constantly mixed with them ; 7th, in no case were 

 dried up, living species (except the pollen and spores), nowhere 

 melted, calcined, or carbonized forms among them ; 8th, even the 

 dust of Genoa, although brought there by the Sirocco, exhibited as 

 little as any of the former, characteristic African forms, which yet 

 are found in every small portion of mud from Africa ; on the con- 

 trary, one of them, Synedra entomon, is a decidedly characteristic 

 South American form. It is remarkable that the few (2 ?) European 

 observations hitherto made have always fallen on the 15th and 16th 

 of May. The author concludes with the question, whether there is 

 not a current of air uniting Africa and America in the region of the 

 trade-winds, which is occasionally, and especially on these days, 

 turned towards Europe, and brings that dust along with it ? 



J.N. 



Observations on the general distribution of Copper and Arsenic. By 

 M. Walchner (from the Comptes Rendus, Septembre 1846). 



From his position as one of the directors of mines in the Grand- 

 Duchy of Baden, M. Walchner had frequently occasion to examine 

 ores of iron, in order to determine their purity, on which the quality 

 of the iron in a great measure depends. " During these researches," 

 he says, " I found that two metals, copper and arsenic, very prejudicial 

 to the quality of the iron, were always mixed with and accompanied 

 in every place the ores of iron dispersed over the whole globe. 

 United in small amount with all the oxides of iron, they occur in 

 every variety of the mines of this metal, and in some in such pro- 

 portions that these mines are wholly unserviceable for the production 

 of iron of a good quality, unless previously purified by a suitable 

 process. 



" Having observed that the natural hydrates of the peroxide of iron, 

 the spathose iron ore, as well as the oolitic and pisiform ores of the 

 Jura formation, which I consider as deposited from ancient chaly- 

 beate springs, contained copper and arsenic, I occupied myself in 

 analysing the ferruginous clays which are the most recent deposits 

 of hydrate of iron formed under our own eyes. The results of these 

 experiments agree with my previous analyses; and even the ores 

 found in peat-bogs and meadows, and formed during the present 

 epoch, contain copper and arsenic. 



" Nothing was now more natural than to look for these metals 

 also in existing ferruginous springs, in the ochres deposited from 

 acidulated waters. Considering that the deposits of iron formed by 

 ancient springs at different far-distant geological epochs contained 

 these two metals, it was necessary to infer, that they should also 

 occur in the ochrey deposits of the present epoch. I therefore en- 

 deavoured to procure the ochres from mineral springs celebrated for 



