302 STRATIGRAPHICAL GEOLOGY 



in three basin-shaped tracts, namely that of Midlothian and Fife 

 on the east, of Lanark and Stirling in the centre, and of Ayrshire 

 on the west. 



Millstone Grit. In the counties of Edinburgh, Fife, Stirling, 

 and Lanark the upper limestones are succeeded by a set of pale red 

 and yellow sandstones in thick beds with occasional layers of shale. 

 This group of sandstones is generally known as the Eoslin Sandstone 

 from its fine exposure near that place. Its thickness near 

 Edinburgh and north of the Forth is from 500 to 600 feet, but 

 it thins from the north-east to south-west ; in Lanark it is only 

 from 90 to 100 feet, and farther west, in Ayrshire, it is so thin as 

 not to be definitely separable from the Coal-measures. 



Eecent examination of the plant remains by Dr. Kidston has 

 led to the recognition of a palaeontological break in this set of 

 beds, 3 and the fact is confirmed by Dr. Traquair's study of the 

 fish remains ; so that the lower part of the Eoslin sandstone is 

 now grouped as " Lower Carboniferous " (i.e. Avonian), and the 

 higher part as " Upper Carboniferous " (i.e. Westphalian). In the 

 Edinburgh district the line of division is drawn near a marine 

 band about 230 feet above the highest limestone. The lower beds 

 include several bands containing marine fossils, and Sphenopteris is 

 the only fern-plant ; while in the upper part plant remains are more 

 abundant, species of Alethopteris, Neuropteris, and Mariopteris being 

 the most frequent with several species of Sigillaria which range 

 upward but not downward. Mr. Arber informs me that as a matter 

 of fact no true species is common to the two floras found in the 

 Eoslin Sandstone. 



Lower Coal-measures. These measures attain a consider- 

 able thickness, about 1200 feet in Fife and Midlothian, from 1200 to 

 1500 in Lanark, and about 1300 in the Clyde Basin. They consist 

 of grey and white sandstones, with shales, coals, fireclays, and iron- 

 stones, and ten of the coal-seams are from 2 to 5 feet in thickness. 

 In Lanark and the Clyde basin the base of the series is taken at the 

 slaty-band ironstone, and there are several other continuous beds of 

 blackband ironstone which are of much commercial importance. 



These measures contain a flora which is pronounced by Dr. 

 Kidston to be the same as that of the Lower Coal-measures of 

 England. The commonest plants are Neuropteris heterophylla, 

 N. gigantea, and Sphenopteris latifolia. They also include two 

 marine bands, one near the base containing Schizodus deltoideus, 

 Conularia quadrisulcata, Lingula mytiloides, and Orbiculoidea 

 nitida ; and another above the " Ell " coal containing the same 

 Conularia and Orbiculoidea with Productus scalriculus, Bellerophon 

 Urei, and Aviculopecten papyraceus. 



