382 The American Geologist. December, iwk/' 
"nephelino-kersantitic" magma of Michel Levy. It is a good 
example of the melanokrate series of Brogger. 
The orthoclase gabbro (Fig. 5) is the only rock of the 
series possessing an appreciable development of the feldspar 
triangle below the x axis — this is its chief characteristic, and 
translates the presence of the orthoclase. The ratio KiO:Na20 
is therefore changed, but scarcely equals i : 2. The ratio 
c : n indicates that the feldspar is a very acid labradorite with 
even perhaps some andesine. CaO still predominates over 
Na.iO and K^O, but the metals Na -r K slightly exceed Ca. 
It is a type which does not fall naturally under any of Rosen- 
busch's magmas, having some of the characters of the grani- 
tic-dioritic magma (c/ ), the gabbro magma (»/) and the peri- 
dotyte m.agma (tt). It is another example of the granito- 
esterellic magma of Michel Levy, and as such it is to be com- 
pared with the diabase (954). The orthoclase gabbro belongs 
to the melanokrate series of Brogger, but dilifers from the pre- 
ceding types since it belongs to the alkaline division. This 
rock belongs to the diorite-diabase type of Lang's calcic class. 
The quartz gabbro (Fig. 9) is markedly more acid than any 
other rock of the series. Its chief characteristic does not. 
therefore, appear from the diagrams so strikingly as in other 
cases. However, it is to be noted that the size of the two tri- 
angles is in general a measure of the basicity, and we see that 
the figure is the smallest of the series. The ratio c : n shows 
that the feldspar is more acid than the prevalent labradorite, 
being chiefly andesine. The excess of calcium oxide ( c ') is 
very slight, and this, together with the low content of iron and 
magnesia, makes the present composition of the rock corre- 
spond to that of a leukokrate. The ratio K^O : Na^O is very 
low — I : 10, and, as in the plagioclasyte, this is caused by an 
increase in the sodium oxide rather than by a decrease in the 
potash. The rock is clearly derived from the granito-dioritic 
magma of Rosenbusch. It furnishes a third example of the 
granito-esterellic magma of Michel Levy, of the diorito-dia- 
basic type ; and belongs to the norite-dolerite type of Lang's 
calcic class. 
The cordierite noryte is a rock entirely peculiar. The 
great excess of alumina, so strikingly exhibited by the dia- 
gram (Fig. 8), shows that it represents a type unknown until 
