FOSSIL ALGsE. 43 



Char a strikes me as much the best claimant until we come 

 to the Tertiary Characece. 



In passing one ought to note the possible Alga of the 

 Oolitic granules at present attracting the attention of many 

 o-eoloo-ists and resembling the Girvanella of Nicholson and 

 Etheridge of Ordovician age, and as Mr. Bullen Newton 

 points out to me the Siphonema of Bornemann which goes 

 as far back as the Cambrian rocks. The best specimens 

 reveal no more than a tubular structure consistent with an 

 organic origin, and however strong the temptation may be 

 to regard them as Algal such recognition must be delayed 

 until better evidence is forthcoming. 



Castracane has stated that he found several species of dia- 

 toms in the ash of English coal and that these are fresh- water 

 forms at present existing. So exhaustive a search has been 

 made, however, by Williamson and other observers that in 

 spite of the fact that Castracane claims to have used due 

 precautions we must treat his record as open to doubt until 

 it is confirmed by further discovery. No diatom appears 

 with this possible exception until we reach the Upper 

 Cretaceous beds, and then they occur again in extensive 

 deposits of Tertiary and Quaternary age. All these fossil 

 diatoms, and they are very numerous, from the chalk down- 

 wards, belong to genera and a large number of them to 

 species now existing, though the proportion of identical 

 species diminishes with the age of the deposit. The forms 

 known as Bactryllium from the Trias may have been ances- 

 tors of the diatoms — it is very doubtful — and but for this one 

 possibility we have no hint of the coming of this type 

 until we find it in a profusion of forms some of which 

 have survived from the Cretaceous age to the present day. 

 One would expect them in the Silurian rocks, but here too 

 there is a blank. Careful search has been made for them 

 by several observers, but the matter is eminently worthy of 

 prosecution and may be urged upon the characteristically 

 industrious diatomist as a more worthy occupation than 

 practical experiments in the origin of species. 



Just as at present the diatoms are engaged in making 

 deep-sea deposits in the colder regions of the northern and 



