EASTERN BORDERS. 293 



the upturned edges of the Silurian formation. These ancient 

 slaty rocks form the Lammermuir hills ; they exhibit many foldings 

 and contortions, and extend across the northern portion of the 

 county, being connected with a range which traverses the 

 island in a south-western direction. The county has been broken 

 through at many points by great masses of porphyritic and trap 

 rocks. 



Now if the coast be traversed from the Tyne to the Aln, there will 

 be seen exposed in the cliffs several series of underclays, coals, shales, 

 and sandstones ; shale-beds near the coal will be found more or less 

 carbonaceous, so much so in some cases, that they may be burnt ; 

 and there will also be observed remains of plants in considerable 

 numbers, imbedded in the clays, shales, and sandstones. At a few 

 points, as at Bondicar, fossil shells will be met with, which had 

 formerly lived in fresh water, for, though not the same species as the 

 Anodons and Unios, or freshwater Mussels now living in our rivers, 

 they resemble, and are nearly allied to, these shells ; but, throughout 

 the whole series of 2000 feet in thickness, not one fragment will be 

 seen which can be attributed to a marine origin. When, however, 

 we pass the Aln, new historical records of the era are presented, 

 indicating the prevalence of different conditions : we have still several 

 series of coal-seams associated with the usual characteristic strata, but 

 interstratified with them are limestones and calcai'eous shales which 

 are crowded with marine relics — wth Corals, Encrinites, Mollusks, 

 Trilobites, and Fish. Successive generations of these animals had 

 lived and died, and been tranquilly entombed under precipitates from 

 the ocean, or among mud which had been carried into it from the 

 land. This complicated series of rocks is the Mountain Limestone 

 formation, and it presents wherever it is found, whether in Northum- 

 berland or Berwickshire, the same assemblage of facts. At two extreme 

 points of the district, whence we derive the materials for our fossil 

 flora, the vniiformity of conditions is not uninterestingly shown. 

 According to Mr. Stevenson, Lepidodendrons and Calamites (plants 

 hereafter to be described) occur at Langton Burn, in Berwickshire, 

 along with Gyracanthus, the spine of a bony fish ; and on Alnwick 

 Moor, in Northumberland, the same plants are found in the sandstone 

 associated with the Gyracanthus Alwicensis of Agassiz. 



The Origin of Coal. 



That coal has been derived from plants which once grew on the 

 surface of the earth can now be conclusively established. This indeed 

 might be inferred from the vast number of fossil plants in beds both 

 below and above a coal-seam. An examinatioii of the cliffs on the sea- 

 coast near to Berwick, at North Sunderland and Howick, and of inland 

 quarries, will discover trunks and branches of trees with the vegetable 

 matter of the interior replaced by sand or mud, but with the original 

 bark converted into coal . The inference is strengthened by a comparison 

 of the composition of living vegetables with that of coal ; for, leaving 

 out accidental and unessential ingredients, both are formed of the 



