554 
of the Galloway chain on the north side of the axis. 5. Unconform- 
able masses of old red sandstone. 6. Coal-basin of Girvan-water. 
7. Fossiliferous slates and limestone rising from under the coal 
series. 
Conclusion.—It appears, from the preceding synopsis, that there is 
a continuous and apparently uninterrupted sequence of deposits 
from the lower beds of the new red sandstone formation to the low- 
est known strata of England; that beds of masses of limestone ap- 
pear here and there in the descending series ; and (with the excep- 
tion of the mountain limestone) that they are neither so continuous 
nor so fixed in their place as to offer any good bases for the general 
classification of the groups; that the divisions into which the de- 
scending series may be separated often pass into one another, so as 
to make their demarcations doubtful or arbitrary; and that, in the 
lower divisions, organic remains gradually disappear. The great 
divisions of the descending series hitherto ascertained are as fol- 
lows :— 
1. Carboniferous.—Passing in some places at its upper limits into 
the lower new red sandstone. 
2. Old red sandstone.-—Passing in its upper limits (Scotland and 
Ireland) into the first division, and including the slate rocks, &c., of 
Devon and a part of Cornwall. 
3. Silurian.—Passing in its upper groups into the old red sandstone. 
All the country described by Mr. Murchison as superior to the Llan- 
deilo flags, separated into three groups—upper, middle, and lower. 
East of Berwyn chain, lower group. North of the Berwyn chain 
(Denbighshire), upper, middle, and lower groups; but with a new 
mineral type, and without any upper bands of limestone. West- 
moreland : upper group largely developed, and including fossils of the 
tilestone ; middle group without limestone bands or fossils ; lower 
group with many characteristic fossils. Horton and Ingleton, mid- 
dle and upper groups. Ireland (Waterford and Kerry), lower group. 
Scotland (Ayrshire), Silurian group, but not defined. 
4. Sub-Silurian, or Upper Cambrian.—The old rocks of South Wales 
below the preceding division ; containing Graptolites, but no well- 
defined calcareous band, and very few fossils. A part of the Berwyn 
chain based on the Bala limestone. The upper part of the roofing 
slates, &c., of Cumberland, immediately under the Caradoc limestone 
(of Coniston, &c.). Slates of Charnwood Forest? Slates of the 
Mourne mountains, of the Galloway chain, &c. 
5. Lower Cambrian.—The great slate group of North Wales be- 
low the Bala limestone. The old roofing slates of Cumberland. 
6. Lower Cumbrian, or Skiddaw slate-—Slates of Skiddaw Forest, 
lower part metamorphic. Provisionally arranged in this place, the 
chlorite slates, &c., of Anglesea and Caernarvonshire. 
A letter addressed to Dr. Fitton, by Mr. Lyell, and dated Boston 
the 15th of October, 1841, was then read. 
Mr. Lyell’s attention, between the period of his arrival in the 
United States and the date of his letter, had been principally devoted 
