Proceedings. 15 
Barmouth. In South Wales at St. David’s, at Shineton not far 
from Shrewsbury, at Malvern, and, lastly, near Carmarthen. 
The true position of the Tremadoc Slates between the 
Lingula Flags below and the Arenig beds above, was first de- 
termined in North Wales, so we will take this district first. 
The beds crop out round the northern part of the Merioneth, 
or Harlech anticline, where they are found always to rest con- 
formably on the Lingula Flags below them, the zone of the 
graptolite Dictyograptus socialis being considered a passage-bed 
between the two series. The upper limit to the beds is diffi- 
cult to determine owing to the unfossiliferous character of 
those which rest upon them. 
On the S. side of the anticline the beds are found near 
Dolgelly and on the flanks of Cader Idris. The beds are 
divided into—Lower Tremadoc, with a thickness of about 
500 ft.; Upper Tremadoe, also with a thickness of about 500 ft. 
The cliffs of Ogof-ddu near Criccieth and the promontory of 
Craig-ddu exhibit a complete section from the Lingula Flags to 
the Upper Tremadoce, but there are no fossils here. Further east, 
however, at Penmorpha, Borthwood, and Portmadoc, and on 
the south side of the estuary at Aber ei Sudhrath and Cae Iago, 
fossils are plentiful. From these beds Mr. D. Homfray, 
Mr. Ash, Mr. Salter, and Mr. Gibbs obtained their rich 
collections of about 42 species. 
The Lower Tremadoc Slates are thin-bedded, fine-grained, 
and earthy, generally grey or biuish in colour, and often 
stained with iron; sometimes the slates are striped by harder 
bands, showing alternations during the deposition of the 
sediment. 
The Upper Tremadoc Slates are more sandy in character and 
greyer in colour, except when ferruginous, often with felspathic 
lines,—a ribbon-slate in fact. 
The most important fossils of the Lower Tremadoc are the 
following :—Niobe Homfrayi, Psilocephalus inflatus and inno- 
tatus, Orthoceras sericeum, Ogygia scutatrix, Dikellocephalus 
furca ?, Conocoryphe depressa. 
Upper Fremadoc Fossils:—Asaphellus Homfrayi, Asaphus 
