240 



THE GEOLOGIST. 



" The Greywacke rock, now tlie Cambrian system of Sedgwick, or 

 Lower Silurian of Murchison, forms the Lammermnir Hills, which 

 range through Berwickshire from east-north-east to west-south-west. 

 On these rocks rest unconformably the upper beds of the Old Red 

 Sandstone, which again are conformably overlaid by the Carbo- 

 niferous formation. The beds of this formation in Berwickshire are 

 connected with those of ISTorthumberland, and then, we find it dis- 

 tinguishable into four groups, which thus succeed each other in 

 descending order : " 1, The Coal-measures ; 2, Millstone Grit ; 3, the 

 Mountain-limestone ; 4, the Tweedian-group. 



" 1 and 2. ISTeither the Coal Measures nor the Millstone-grit ex- 

 tend into Berwickshire ; but it may be here observed 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 quality, or so numerous, as in the Newcastle Coal-Field. 



" 3. The Mountain-limestone spread over a large area in ISTorthum- 

 berland, but a few only of the lower beds appear in Ber'^'ickshire, 

 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 Lammerton Shell, 

 and on the north side of the range they overlie the Tweedian gToup 

 from the Cove harbour at Cockburnspath to the northern extremity 

 of the county at Dunglas Burn. 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 Pro ductal and Encrinal Mountain-limestone of Northumberland 

 and Berwickshire. They consist of grey, greenish, and lilac coloured 

 arenaceous shales, interstratified with sandstones usually yelloTNdsh 

 or white slaty sandstone, and thin beds of argillaceous and magTiesian 

 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, Modiolge and Entomostraca are 

 tolerably abundant in some beds : but at Tweed Mill, species of 

 Ortliocerata and Pleurotomaria are associated with coniferous trees. 

 The group is specially marked by the absence of Brachiopoda, wlrich 

 are very abundant in the overling 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 accompanied with land 

 plants, which show that the deposit was formed in a shallow estuaiy. 



* Transactions of Bcn^Ticksliiro Club, vol. iii., p. 172. 



(To be continued.) 



