662 DR. C. CALLAWAY ON THE [Noy. 1902, 
30. A Descriptive OUTLINE of the Piutonic Compiex of CENTRAL 
Anetssey. By Cuaries Cattaway, D.Sc., M.A., F.G.S. (Read 
_ June 11th, 1902.) 
[Map on p. 664.] 
ContTENTS. 
I. Introduction 
II. The Materials which compose the Plutonic Complex ...... 663 
(1) The Diorite and its Modifications. 
(2) The Felsite and its Modifications. 
(3) The Granite (Haplite) and Quartz-Felsite. 
III. The Relations of the Rock-masses ............scescseeseesserees 669 
(1) The Relations between the Diorite and the Granite. 
(2) The Relations between the Felsite and the Granite. 
(3) The Relations between the Felsite and the Diorite. 
TY. Summary of Results. isliccc-cese-ctcccaaceeteestvae see meat 679 
I, Lyrropvuction. 
TWENTY-TWO years ago, a paper by me on ‘Some New Points in 
the pre-Cambrian Geology of Anglesey ’ appeared in the Geological 
Magazine.! One section of that paper discussed the ‘ Continuity of 
the Granitoid Series with an underlying Gneiss,’ and the chief 
evidence for that continuity was furnished by the Craig-yr-Allor 
anticline. An ellipsoidal dome of hornblendic and chloritic gneiss 
in Central Anglesey was described as surrounded by ‘ granitoidite,’ 
below which it appeared to dip in a quaquaversal manner. As 
both the gneiss and the granitoid rock were then generally 
regarded as of sedimentary origin, the inference that the gneiss 
represented a formation older than the ‘ granitoidite’ appeared 
to be justified. We now know, however, that these rocks are not 
metamorphosed sediments, but plutonic masses; therefore they 
can never have been in stratigraphical sequence. A review of the 
ground in the light of the new theory of origin has now been 
undertaken, and the following paper is the result. J include within 
its scope the acidic rocks, both massive and schistose, which are 
associated with the gneisses and granite, so as to present a general 
outline of the structure of the plutonic complex of Central 
Anglesey. I do not propose to enter into minute petrographical or 
geognostic details: the former being unnecessary for my purpose, 
while the latter would be superseded by the expected mapping of 
Mr. Edward Greenly. Some corrections were made in the old inter- 
pretations of the district by the Rev. J. F. Blake*in 1888. In 
1 Dee. 2, vol. vii (1880) p. 117. 
2 Quart. Journ. Geol. Soc. vol. xliv (1888) p. 463. Details will be given 
further on (p. 671). 
