240 
THE GEOLOGIST. 
" The Greywacke rock, now the Cambrian system of Sedgwick, or 
Lower Silurian of Murchison, forms the Lammermuir Hills, which 
range thi'ough Berwickshii-e from east-north-east to west-south-west. 
On these rocks rest unconformably the upper beds of the Old Red 
Sandstone, whicli again are conformably overlaid by the Carbo- 
niferous foiTnation. The beds of this formation in Berwickshire are 
connected with those of Northumberland, and then, we find it dis- 
tinguisliable into four groups, which thus succeed each other in 
descending order : " 1, The Coal-measures ; 2, Millstone Grit ; 3, the 
Mountain-hmestone ; 4, the Tweedian-gi'oup. 
" 1 and 2. Neither the Coal Measures nor the Millstone-grit ex- 
tend into Berwickshire ; but it may be here obsei-ved that the term 
Coal Measures is objectionable, because both the Millstone-grit and 
the Mountain-limestone contain coal-seams, though not so thick, so 
good in quaHty, or so numerous, as in the Newcastle Coal-Field. 
" 3. The Mountain-limestone spread over a large area in Northum- 
berland, but a few only of the lower beds appear in Berwickshire, 
and they form a very small portion of the county. On the south 
side of the Lammermuir they occupy a narrow strip along the coast, 
from the mouth of the Tweed to a little beyond Lammei-ton Sheil, 
and on the north side of the range they overlie the Tweedian gi-oup 
from the Cove harbour at Cockburnspath to the northern extremity 
of the county at Dunglas Bum. Brachiopods and other fossils, 
characteristic of the mountain-limestone, occur in these beds. 
" 4. In 1856* I applied the term, " Tweedian-group" to a series of 
beds lying below the Mountain-limestone. They form, as I then 
stated, the lowest portion of the Carboniferous formation, lying below 
the Productal and Encrinal ]\Iountain-hmestone of Northumberland 
and Berwickshire. They consist of grey, greenish, and lilac coloured 
arenaceous shales, interstratified with sandstones usually yellowish 
or white slaty sandstone, and thin beds of argillaceous and magnesian 
limestones. Lepidodendra, coniferous trees, and Stigmaria fucoides 
occur in some parts of the group, but there are no workable seams of 
coal. Scales and remains of fish, Modiola3 and Entomostraca are 
tolerably abundant in some beds : but at Tweed Mill, species of 
Orthocerata and Plem-otomaria are associated with coniferous trees. 
The group is specially marked by the absence of Brachiopoda, which 
are very abundant in the overlying mountain-limestone — generally 
freshwater or lacustrine conditions are indicated : there is no 
evidence of a deep sea deposit, and in the rare instances where we 
find undoubted marine remains, they are accomjaanied with land 
plants, which show that the deposit was fonned in a shallow estuary. 
* Transactions of Bcrwicksliii-e Club, vol. iii., p. 172. 
(To he continued.) 
