_ 
ON THE CRYSTALLINE ROCKS OF ANGLESEY. 165 
No. 5574. 
7 S.E. Cromlech. 
SiO, . 
Al,O, 
Fe,O, 
FeO . 
MnO 
CaO . 
MgO . 
K Om 
Na,O . : . 
H,O (at 110° C.) 
H,0O (above 110°) 
Hornfels. 
Bodafon Mountain. 
IE, 
58°52 
23°40 
3:02 
2°30 
Noe 
99°67 
peace 
He oo 
Hane 
99-68 
This rock completes the series from the hornfels associated with the 
granite. The high alkali percentage in some of these suggested doubts 
as to whether they could be of sedimentary origin. The alkalies are, how- 
ever, quite as high in this rock, and of its sedimentary origin there can 
be no doubt, the evidence in the field and under the microscope being 
decisive. It is from the beds which pass under the great quartzite of 
Bodafon Mountain, and was obtained in a small quarry which was made, 
with most fortunate results, right through the junction, in the spring 
Dolerite. 
22N.W. Boss S.W. of Bryn Lhvyd. 
of 1908. 
No. 1074. 
i 
BiO>, a. ; : 47°43 
iO}. 7: ‘ : trace 
AlLOpres : : 17-58 
Hes0} : d 2°08 
FeO). : : 7-45 
Nao). : é trace 
CaO’. : ; 10-92 
MgO . , - 6-71 
EO), : 2 trace 
NaSO- 5 : ; 3°89 
HZO(at 10a) 0-25 
H,0 (above 110°) . 2°65 
315 le le ES 0°53 
99°49 
ils Ill. 
47-47 
3°50 
99°56 
ie 
4:23 
No. 1074.’ This is the pillow diabase lava of the Newborough 
district, from the best sections, where it is quite undeformed and 
unaltered. 
No. 518A, 
22 8.  Cerig Mawr. 
SiO, . 
Al,0, 
Fe,0,. 
Alkalies 
Jasper. 
In Ellipsoidal Diabase. 
lr 
88:01 
1:36 
10°68 
None 
100°05 
