A. R. Andrew—The Dolgelley Gold-beit. 161 
Within the last ten years, however, Professor Lapworth and 
Dr. T. Stacey Wilson have mapped much of the Merionethshire 
country and determined the sequence and general distribution of 
the various lithological groups of the Lower Cambrian of the region. 
Although their work has not yet been published, they permitted me 
to use their results and showed me through their succession from the 
Cefn Slate Group to the top of the Vigra Beds. The following is 
the descending: sequence of Lapworth and Wilson as employed and 
referred to by myself in the present paper :— 
9. Ffestiniog Beds of Belt. 
rs 8. Pen Rhos Beds (Upper Maentwrog of Belt): Dark-blue slates 
sae eee characteristically weathering to a bright-red or perhaps rusty 
Geological _ colour. Ae 
Survey. 7. Vigra Beds (Lower Maentwrog of Belt): Dark-grey and blue 
slates, with numerous interstratified hard beds of felspathic 
4 and siliceous material, which occur throughout. 
Menevian of (6. Clogau Beds (Menevian of Salter and Belt): Black shales and 
Survey. slates. 
5. Gamlan Shale Group: A succession of grey, greyish-green, and 
sometimes purple shales, slates, and flags, interbedded with 
occasional grit bands, which increase in number and thickness 
on going eastwards ; thickness 750 to 1200 feet. 
4. Barmouth Grits: Massive felspathic grits or greywackes with 
pebble bands ; say 600 feet thick. 
Hafotty or Manganese Shale Group (with the well-known 
! persistent zone of manganese ore at the base): Grey and 
Harlech Grits green shales and flags; to the west with rare grits; to the 
of Survey. east the grits become more frequent and eventually coarse 
and thick-bedded ; total thickness about 1000 feet. 
Rhinog Grits: Massive grits forming the Rhinog and other 
mountains ; thickness about 2500 feet. 
1. Cefn or Llanbedr Slate Group: Blue and purple shales, flags, 
and slates; to the west (Kgryn, Llanfair) with occasional 
grit bands; to east (Cefn Cam, etc.) the grits are more 
abundant, and the lowest beds (Dolwen) are red felspathic 
grits and shales. 
Paleontology.—The district around Dolgelley had always been 
considered destitute of fossils until in 1864 Readwin found 
Paradoxides Davidis, which was described by Plant (22). This, 
together with the discovery of Anopolenus and Theca, enabled the 
lower beds in which they occur to be cut off from the higher beds in 
which are found the Olenus and Lingula of the Survey. In 1866 
Plant discovered a considerable number of fossils (21-3). In 
1867 Belt’s examination led to the discovery and identification of 
many additional genera and species (24). Many fossils too had been 
discovered by the officers of H.M. Geological Survey. The following 
table contains the names of all fossils that have been discovered in the 
Dolgelley area and in the immediately neighbouring country. In 
this list ‘P’ means that the fossil was reported by Plant, ‘B’ by 
Belt, ‘S’ by the Survey. 
From the Ffestiniog Group of Belt ; the Hafod Owen of Plant. 
-B_ Conocoryphe micrura (Salt.) (from B,P,S Lingulella Davisii (McCoy). 
ise) 
bo 
Upper Ffestiniog). B Bellerophon cambrensis (Belt) 
P Conocoryphe sp. (from Upper Ffestiniog). 
B,S Hymenacaris vermicauda (Salt.). P Buthotrepis (?). 
P Olenus sp. 
DECADE V.—VOL. VII.—NO. Iv. 11 
