FOSSIL DEPOSITS OF DIATOMACE^E. 



313 



Mourne in Ireland (Fig. 145), and in the island of Mull in Scot- 

 land. Similar deposits in Sweden and Norway are known under 

 the name of berg-mehl or mountain-flour ; and in times of scarcity 

 the inhabitants of those countries are accustomed to mix these 

 substances with their dough in making bread. This has been 



Fig. 145. 



Fossil Diatomacece, &c.,from Mourne mountain, Ireland :— a, a, 

 a, Gaillonella (Melosira) procera, and G. granulata ; d, d, d, G. 

 biseriata (side view) ; 6, b, Surirella plicata ; c, S. craticula ; k, 

 S. caledoniea ; e. Gomphonema gracile ; /, Cocconema fusidium ; 

 g, Tabellaria vulgaris ; h, Pinnularia dactylus ; i, P. nobilsi ; I, 

 Synedra ulna. 



supposed merely to have the effect of giving increased bulkto their 

 loaves, so as to render the really nutritive portion more satisfying ; 

 but as the berg-mehl has been found to lose from a quarter to a 

 third of its weight by exposure to a red -heat, there seems a strong 

 probability that it contains Organic matter enough to render it 

 nutritious in itself. When thus occurring in strata of a fossil 

 or sub-fossil character, the Diatomaceous deposits are generally 



