42 Reports and Proceedings—Geological Society of London. 
Wansbeck about 15 miles above Morpeth. It is intruded along 
a fault-fissure in beds of Bernician age, and apparently comes to 
a natural head. The basalt is characterized, microscopically, by 
narrow lath-shaped felspars and curved augites. Macroscopically, 
its most interesting feature is the occurrence of large inclusions of 
a felspar, which is shown by chemical analysis to be closely allied 
to anorthite. The exterior of the inclusions in contact with the 
ground-mass is strongly zoned, the latter showing a slightly chilled 
edge; the individual crystals are intergrown and are cracked, faulted, 
and in places completely shattered. In no case is the dislocation 
great, and, in fact, the crystals seem to have burst in situ. These 
phenomena point to a plutonic origin of the felspathic inclusions and 
connect them with the porphyritic felspars of the Tynemouth 
Dyke, for which a similar origin has already been suggested by 
Dr. Teall. 
The dyke which comes to a head in the coast-section at Collywell, 
about 24 miles distant, shows almost precisely the same peculiarities. 
Chemical and microscopical examination of the two basalts and their 
felspathic inclusions show them to be practically identical. Con- 
sidering these facts and the general field-relationships of the dykes, it 
appears probable that they belong to the same intrusion. 
The work of Dr. Teall upon the dykes at Tynemouth and Morpeth 
has been amplified by further observations. The resemblances among 
the four dykes are so strong as to render it probable that they are 
derived from a common source. The observed differences are such as 
could be readily accounted for by differences of physical condition 
operating during the period of consolidation of the dykes. 
December 1, 1909.—Professor W. J. Sollas, LL.D., Sc.D., F.R.S., 
President, in the Chair. 
The following communications were read :— 
1. ‘‘The Tremadoc Slates and Associated Rocks of South-East 
Carnarvonshire.”” By William George Fearnsides, M.A., F.G.S., 
Fellow of, and Lecturer in Natural Sciences at, Sidney Sussex 
College, Cambridge. 
This paper gives the results which have been obtained by the 
author in making a detailed map of the country about Portmadoc, 
Tremadoc, and Criccieth in Carnarvonshire, and describes the 
stratigraphy of the Cambrian and Ordovician rocks there exposed. 
The area described includes the original type-area of the Tremadoc 
Slates (Sedgwick & Salter), and the paper includes a detailed account 
of the local development of this well-known series. 
The first part of the paper is devoted to a brief summary of the 
results attained by former workers, and is arranged to show the 
various stages through which the nomenclature of the major sub- 
divisions of the Cambrian and Ordovician Systems have evolved. 
The sedimentary series are described in the order of their formation. 
The succession may be tabulated as follows :— 
