296 Proceedings of the Royal Society of Edinburgh. [Sess. 
4. Quantitative Chemical and Mineral Characters. 
In the accompanying table are listed four full analyses (Nos. 1, 2, 6, 10) 
and two partial analyses (Nos. 3, 5) of the series of rocks treated in this 
paper. For comparison are added analyses of albite-trachyte of Skomer 
Island, Pembrokeshire (No. 4), and of three bostonitic rocks from the 
Kristiania district of Norway (Nos. 7, 8, 9). Each of the four groups into 
which the series has been divided are represented. The albite-bostonites 
are represented by two complete analyses of lavas from South Bute ; the 
bostonites by a partial analysis of a sill from Great Cumbrae island ; the 
quartz-keratophyres and felsites by the analysis of a felsite from the 
Campsie Fells, near the Meikle Bin vent; and the phonolites by an analysis 
of the well-known rock of Fintry. The arrangement of the analyses is 
roughly from a great excess of soda over potash towards equality of these 
constituents or slight dominance of the potash. 
The principal features of all the analyses are relatively high silica and 
high alkalies, with insignificant ferrous iron, magnesia, and lime. This 
of course expresses the fact that the rocks are highly felspathic. The 
alumina diminishes in the albite-bostonites (Nos. 1, 2), and in the quartz- 
rich rocks (Nos. 9, 10), relative to the bostonites and phonolites (Nos. 6, 7, 8). 
With regard to the relations of soda and potash, the albite-bostonites show 
a decided predominance of soda — that is, in the terminology of the American 
Quantitative Classification, the rocks are dosodic ; but in the other rocks 
the alkalic oxides are approximately equal — that is, the rocks are sodi- 
potassic. These facts are perhaps better expressed in the consideration 
of the norms. In many of the rocks ferric oxide is considerably in 
excess of ferrous oxide, a fact probably due to hsematisation of the mafic 
constituents. 
The Norms . — The norms, as calculated by the methods of the American 
Quantitative Classification, give results that express quite nearly the 
actual mineral composition or mode of the rocks. Table II gives the 
norms, with the rocks arranged in the same order as in Table I. 
A general consideration of the norms shows that the rocks are highly 
felsic, as is shown by the figures expressing the ratio between the salic 
and femic minerals. All the rocks thus fall on or near the border-line 
between Classes I and II in the American Quantitative Classification. 
This is expressed by the frequency of bracketed numbers in the first 
figure of the symbols for the rocks (see Table I). Quartz is relatively 
abundant in the albite-bostonites, and in the felsitic rocks (1, 2, 4, 9, 10); 
but there is a deficiency of silica in the phonolites and bostonites, so 
