Vol. 58.] THE PLUTONIC COMPLEX OF CENTRAL ANGLESEY. 665 
About 2 furlongs! to the west, on the northern side of the road, 
is a long section of rock much of which is similar to the last; but 
some of - it is sounder, there is more foliation, and eranite-veins are 
more numerous. 
(ec) Micaceo-chloritic eu oneal a quarry on the Holy- 
head Road, 14 furlongs east of the ;* milestone, the rock is of a 
greenish colour and rather micaceous, It is penetrated by veins 
and small masses of granite. The structure is rather massive, dips 
being indistinct. A small quarry displays similar rock 100 yards 
to the west-north-west. Half a mile to the south-west, close to 
the southern junction with the granite near Boleyn, there is a 
good quarry-section of rock of the same general type, but it is more 
micaceous, and displays a clear foliation-dip. A thin slice of this 
rock (57 8) shows under the microscope irregular fragments of 
felspar, in a chloritic groundmass. Several parallel flakes of a white 
mica cross the field, and part of the chlorite is orientated in the 
same direction. Some secondary quartz is present. This schist is 
apparently formed from the diorite, but the rock has undergone 
partial reconstruction, probably under the influence of the adjacent 
granite. Prof. Bonney remarks of this specimen that ‘the rock 
was very probably once igneous.’ 
(qd) Kersantite and biotite-gneiss.—Biotite is normally 
developed in the diorite, whenever granite-veins come in abundantly. 
We thus get a kersantite where the rock is massive, and a biotite- 
gneiss where foliation is produced. These effects were described by 
me in 1887,? and have been noticed by other writers.’ The 
evidence, so far as Anglesey is concerned, will be offered on 
p. 669. 
(2) The Felsite and its Modifications. 
I have never succeeded in obtaining a specimen of the felsite in 
its original state. The least modified specimen has been recognized 
under the microscope by several experts as a true felsite.’ A 
chemical analysis of the rock, taken at a distance of 2 feet from 
the above in the same unbroken mass, has been kindly made for 
me by Mr. Philip Holland, F.1.C. It is slightly schistose, and 
indicates an early stage of the transition from the felsite to mica- 
gneiss. I have placed by the side of it an analysis of a rhyolite 
* Localities and distances are taken from the 6-inch Ordnance-map. 
* Rep. Brit. Assoc. 1887 (Manchester) p. 706. See also Quart. Journ. 
Geol. Soc. vol. xlv (1889) pp. 478-87 & Clean ‘Mag. 1894, pp. 217-19. In the 
Malvern rocks, hornblende is sometimes (at least) changed to black mica, through 
the intermediate stage of chlorite. I do not know whether chlorite has been 
changed into biotite in Anglesey, as I have not been able to work out the genesis 
of the mica so completely as at Malvern. 
’ KE. Hill & T. G. Bonney, Quart. Journ. Geol. Soc. vol. xlviii ree) pp. 128- 
32, 135-37 ; J. Parkinson, zbid. vol. lv (1899) pp. 440-43, 445; G. A. J. Cole, 
‘Trans. Roy. Irish Acad. vol. xxxi (1900) pp. 449, 453 et seqq. 
* Quart. Journ. Geol. Soe. vol. lii (1897) p. 351. 
