380 
THE CARBONIFEROUS VOLCANOES 
BOOK VI 
A number of specimens selected as illustrative of the different varieties 
have been analyzed and the results are stated in the subjoined table ^ The 
specihc gravity of the rocks is about 2-6. 
1 
SiOa j AI3O3 
Fe^Oa 
FeO 
MnO 
CaO 
MgO 1 KoO 
XanO 
HoO 
Total 
Pepper Craig . 
Kae Heughs 
62-61 
61-35 
18-17 
16-88 
0-32 
0-41 
4- 25 
5- 01 
0-21 
0-26 
2-58 
2-39 
0-74 4-02 
0-44 6-12 
6-49 
5-26 
0-80 
1-70 
100-19 
99-82 
Hopetoun Monument 
Phantassie 
Bangley Quarry 
62-50 
59-50 
58-50 
18-51 
18-25 
21-12 
4-39 
4-81 j 2-34 
4-68 I ... 
... 
2-00 
2-10 
3-70 
0-61 16-31 
0-70 6-30 
0-93 !5-84 
3-44 
5-03 
3-90 
2-10 
1-60 
2-00 
99-86 
100-63 
100-67 
Ihe microscopic characters of these rocks, as worked out by Dr Hatch 
show them to be well-marked and wonderfully fresh sanidine- trachytes’ 
Some of them are porphyritic, with large crystals of perfectly unaltered 
sanidine sometimes also oligoclase. Small but well-formed crystals of 
yellowish-green aiigite, in addition to the porphyritic felspars, are imliedded 
in a hne groundmass composed chiefly of inicrolites of sanidine, but 
with granules of aiigite and magnetite plentifully interspersed, and occasion- 
a y prisms of apatite. There is a group in which the porphyritic felspars 
aie scarce or absent. In these there is little or no ferro-magnesian con- 
s 1 lien ther trachytes, rather less basic than the aiigite-bearing varieties 
Garleton Hills district, and are 
reieiied to in the following section (e).^ 
(e) Eqcks 01 - THE Hecks— In the necks connected with the plateaux 
0 ei types of massive rock are to be found. Among these perhaps the most 
reqiient are trachytes, gi-ey to pink in colour, but apt to weather yellow 
exceedingly compact, sparingly porphyritic, and with a iieciiliar platy 
structure and waxy lustre, liocks of this character also appear as sills and 
dykes. Other varieties that occur in similar positions are more basic in 
com],TOSition, including dark, coarse, granular diabases. In the Jedburo-h 
district the most frequent rocks are beautiful varieties of olivine-doleriTe 
and ohvine-basalt, which form most of the prominent hills of the neighboiir- 
lood.^ These bosses are sometimes associated with agglomerates as at 
In the Oarletoii Hills district, some of the necks present another petro- 
graplncal type which directly connects them with the remarkable lavas of 
he higher part of that plateau. Thus the rock of Traprain Law was ascer- 
ciiied by 1)1. Hatch to be a true phonolite. In its general platy structure 
mid sonorous ring under the hammer it reminds one of typical phonolites. 
ncer le microscope the rock is found to consist mainly of small lath- 
shaped crystals of sanidine arranged in a marked minute flow-structure, but 
wi h few porphyritic crystals. It contains small crystals and ophitie patches 
‘‘"'‘h-ses (ire by Mr. J. S. Grant Wilson, the last two by Mr A Dick inn 
and that h-om Hopetonn Monument by Mr. G. Barrow. Trans. Jioy. Soo. ml yol'. xxxvii n 122’ 
t or fuller petrographieal details consult Dr. Hatch’s paper above cited ^ 
