62 



more highly developed, than those in a manuscript of the first century. 

 The fossils in the Upper Silurian are higher in character than those of 

 the far older Skiddaw Slate period. 



Ar^ain vre find another gap in our records ; those internal forces be- 

 fore spoken of begin to re-assert themselves, but being unable to burst 

 through their rock-bound prison, produce a vast and probably slow up- 

 heaval, throwing the various deposits forming our volumes one, two, and 

 four, into great ciu-ves and contortions, a large portion being denuded and 

 swept away as bed after bed is brought within the range of marine and 

 atmospheric action, so that finally, even the lowest of these deposits is 

 once more exposed to daylight, and a table-land, formed of the older 

 rocks, appears as the nucleus of the future mountain district (fig. 3). 



Around this early nucleus are heaped up in certain areas great thick- 

 nesses of conglomerate and breccia, some of the stones of the latter 

 perhaps indicating a more or less glacial character of climate, and these 

 conglomeratic deposits are succeeded by those of the great Carboniferous 

 period, formed in the seas surrounding the embryo mountain district, and 

 affording evidence of a warm and more genial condition of things — our 

 volume six. Here also we find that the fossils entombed in this series of 

 rocks are greatly different from those found in the leafy deposits of volume 

 four. The sixth century characters differ markedly from those of the 

 fourth ; but let us remember that in some other library, in some other 

 district, fifth century manuscripts are preserved, containing those tran- 

 sitional forms of character, of organic life, which are missing in our own 

 neio-hbourhood. Thus do physical evidence -and the varied phases of 



