23 



either in vast quantities of vegetable matter, swept into some shel- 

 tered hollow in the original estuary, or in a horizontal displacement, 

 which has thrown several contiguous beds over one another.* The 

 strata are displaced by two faults, one throwing the beds down 30 

 feet, and the other 50, in a direction nearly vertical. 



19. The inferior marine groups appear to the south, south-east and 

 south-west of the fresh-water series, and descend in the usual alter- 

 nations to contact with the old red sandstone along the borders in 

 that direction. To the south-east of this border, in Lesmahagow 

 parish and adjoining tracts, a small coal field occupies an isolated 

 position, cut off on the one hand from the Clyde basin, and on the 

 other from the Ayrshire fields, by ridges of Devonian rocks, amid 

 which igneous products are variously intercalated. The strata of the 

 Glenbuck field rise up over a ridge of 1,000 to 1,200 feet high, pass 

 down into the basin of the Douglas, a tributary of the Clyde, and 

 rest on a narrow band of old red sandstone, which cuts them off from 

 the Lesmahagow field ; the latter is separated from the Clyde fields 

 by a similar band to the north-east of the village of Lesmahagow, 

 and stretches out east to near the base of Tinto. The strata are 

 extremely well exhibited in natural sections, and contain a complete 

 suite of fossils of true carboniferous types. " The coal shales, sand- 

 stones and ironstones, afford similar remains in abundance ; and there 

 can be therefore no doubt that the coal of this field is of the same 

 age as that of the Clyde basins. It is worthy of remark, that seve- 

 ral species of Trilobites occur in the shales and limestones, far up in 

 the series ; that a white grit, resting on one of the lower limestones, 

 contains a prodigious quantity of fish remains, and corresponds appa- 

 rently with the great ' fish bed' of some English fields ; and that 

 from one of the middle shales a fossil has been obtained agreeing ex- 

 actly with the Serpulites longissimus of the Silurian System, pi. v., 

 fig. 1. The field contains fifteen seams of coal, whose thickness varies 

 from 2 feet to 15 feet, the aggregate amounting to about 65 feet 

 of workable coal. There are black band and clay band ironstones, 

 the principal seam of the former averaging 11 inches ; but neither 

 these nor the coal beds have yet been worked to any considerable 

 extent, owing to the greater accessibility of the fields farther down 

 the Clyde." f Here, as in other districts, the alternations of lime- 

 stone and the other measures already noticed descend to the horizon 

 of the Old Eed, on which the whole series reposes, without the inter- 



* See Niccl's Geology of Scotland, p. 99, for an illustrative cut, copied from Williams' 

 Mineral Kingdom, vol. ii., p. 319. 

 t See Brit. Assoc. Rep., 1850, p. 77. 



