1915-16.] Trachytes of Clyde Carboniferous Lava-Plateaus. 299 
potassic (bostonites, phonolites, felsites), and therefore fall into subrangs 
3 and 4 in the American Quantitative Classification. 
The norms are less satisfactory in indicating the nature of the mafic 
constituents of this series of rocks. As a matter of fact, the nature of 
the original ferromagnesian minerals can rarely be determined, at least 
in the Scottish rocks, from microscopic examination. A green soda- 
pyroxene occurs but rarely; but it is probable that it was originally 
present in most of the Scottish rocks described. Titaniferous magnetite 
occurs to the extent of about 5 per cent. ; and the abundance of ferric 
oxide as an alteration product or staining material is indicated by the 
presence of haematite in the norm. 
I am much indebted to W. R. Smellie, M.A., B.Sc., and J. V. Harrison, 
B.Sc., for the loan of slides, and the use of chemical analyses prepared 
for or by them in furtherance of their own work, to which acknowledg- 
ment has been made in the course of this paper. 
{Issued separately February 6 , 1917 .) 
