160 A, R. Andrew—The Dolgeliey Gold-belt. 
mining of the district under review. A brief résumé of this literature 
will now be given, and a full list of references will be found at the 
end of this paper. 
Stratigraphy.—The rocks of the district were first mentioned by 
Murchison (7) and Sedgwick (3), and formed part of the formations 
under dispute in the famous Cambro-Silurian controversy. Sedgwick’s 
final classification was as follows, and in so far as it applied to the 
rocks of the Gold-belt it is that accepted to-day :— 
3. Bala Group (Upper Cambrian). 
2. Ffestiniog Group (Middle Cambrian) . . (¢) Arenig Slates. 
(6) Tremadoc Slates) which form 
(a) Lingula Flags \ the Dol- 
1. Longmyndand Bangor Group (L. Cambrian) .  (¢) Harlech Grits gelley area. 
(o) Llanberis Slates. 
(a) Longmynd Slates. 
Between 1850 and 1854 the whole of this Merioneth area was 
mapped by the officers of the Geological Survey, and in 1854 appeared 
their geological maps (on a scale of 1 mile to 1 inch): these have not 
yet been revised (11). In 1866 there appeared the first edition of the 
Geological Survey Memoir of the district (12). A new edition of this 
memoir, published in 1880 (18), contained some changes in the 
classification employed. The Tremadoc Slates were separated from 
the Lingula Flags, with which they had previously been associated, 
and at the same time the term Menevian was first used by the Survey, 
for the band of black shales and slates at the base of their former 
Lingula Flags. The sequence of the Survey became— 
4. Tremadoc Slates . : A A ; Upper Cambrian. 
3. Lingula Flags , : : : : Upper Cambrian. 
2. Menevian Slates . : 5 ; : Middle Cambrian. 
1, Cambrian Grits and Flags - : Lower Cambrian. 
From 1846 to 1867 a certain amount of investigation was carried 
out, chiefly by Sharpe (16), Readwin (29), Salter (20), Plant and 
Williamson (23), Belt (24). Most of these investigations resulted in 
proposals of new classifications of the rocks, but on the whole these 
proposals have not been accepted. The chief of the investigators was 
Thomas Belt, who introduced the splitting of the Lingula Flags into 
the Dolgelley, Ffestiniog, and Maentwrog divisions—a grouping which 
is in use to-day. Belt’s sequence consisted of— 
10. Tremadoc Slates. 
8 and 9. Upper and Lower Dolgelley. 
7. Upper Ffestiniog: Tough blue-grey flags. 
5 and 6. Lower Ffestiniog: Blue and brownish-grey fine-grained flags, the lower 
part slightly arenaceous and micaceous. 
3 and 4. Upper Maentwrog: Dark-blue slates weathering rusty, the lower part 
yellowish and bluish -grey fine-grained flags, sometimes a little 
arenaceous, but not so coarse as the groups still lower. 
land 2. Lower Maentwrog: Blue-grey and blue-black jointed slates with slightly 
arenaceous flags, the lower part grey, and yellowish-grey pyritic flags 
with hard felspathic bands. 
0. Lower Cambrian, consisting of— 
(c) Menevian with Paradowxides. 
(b) Harlech Grits. 
(a) Bangor Slates. 
From 1867 to the present day, except the second edition of the 
Survey Memoir, 1881, nothing additional has been published. 
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