PETROLOGY. 
Norms of Roman Rocks Continued. 
153 
34 
35 
36 
37 
38 
39 
40 
41 
42 
43 
44 
Q... 
Or... 
14.5 
8 i 
o 6 
Ab 
An . 
12 8 
15 6 
12 8 
8 6 
Lc 
23.5 
21.8 
26 6 
16 6 
U 8 
Ne . . 
12 8 
12 8 
6 8 
4 8 
HI... 
Th 
C 
Ac 
Di... 
21.8 
21 .7 
22.5 
17.9 
27.8 
16 i 
Hy 
Wo 
Ol 
5.6 
6 3 
6 i 
15 6 
8 2 
Am 
Mt 
3.9 
7-2 
5-i 
3-7 
3-5 
4-4 
4-9 
5-8 
5-8 
4.4 
6.0 
Hm 
0.8 
2-3 
Ap 
1.3 
o.g 
1.3 
1.8 
0.6 
Rest 
0.5 
100.8 
99-6 
99-8 
IOO.I 
99.6 
IOO.2 
99-8 
100.4 
100.7 
IOO.I 
100.8 
The first fact, and one of the most striking to be noted, is the rarity of quartz. 
This mineral is found only three times, in one case in notable amount in harzose, 
once in shoshonose, and again in negligible quantity in a ciminose. The feldspars 
make up very large percentages of nearly all the norms, except in the salfemanes 
(39-44) where they are largely replaced by lenads. Of the feldspars orthoclase 
and anorthite are the most constant, the former vanishing only in albanose 
(III. 8. 2. 2), and the amount of anorthite being negligible only in phlegrose (I. 5. 
i. 3), beemerose (I. 6. i. 3), and appianose (I. 7. i. 3). It is worthy of note that 
the amount of this anorthite molecule is remarkably constant, for the most part 
about 12 or 13 per cent, though it may be higher or lower. Albite, on the other 
hand, while present in large amount in the persalanes (except appianose) and in 
the dosalanes belonging to the perfelic order germanare, disappears in the rocks 
of this latter class as soon as the lenads increase to notable amounts in vicose (II. 
6. 2. 2), and from this on it is n3t found in the norm. With few exceptions it is 
very subordinate to orthoclase, though this is compensated for in many cases by 
the amount of nephelite. 
Correlated with the poverty of the magmas in normative quartz (excess of 
silica) is the almost invariable presence of lenads, either nephelite or leucite or 
both. Apart from the norms which are quaric (15, 18, and 28), and where they 
can not exist, lenads are absent only in the norm of one rock, No. 17. Leucite is 
absent from the norms of all the persalanes except appianose, as well as from the 
perfelic dosalanes, and begins to appear in vicose (in which concomitantly norma- 
tive albite is absent), whence to the most femic rock it is a constant normative 
constituent. Nephelite, on the other hand, is present in all the norms, except the 
five spoken of above, in which lenads are not present, and from vicose to albanose 
