EXCURSION II. 71 



surged they ever so fiercely, could shift the position of such 

 a mass ; and we must therefore conclude that the huge 

 boulder now rests where it was originally thrown down by 

 the glacier or floating berg, which bore it from the granite 

 nucleus. Perhaps, however, it is not necessary to suppose 

 that the dike was then excavated to its present level. It is 

 quite conceivable that as the parts of the dike around the 

 boulder were worn away, its support may have been loosened, 

 and so its position may have shifted a little at long intervals. 

 35. In the sandstone of the cliffs overlooking this point we 

 were so fortunate as to discover a true carboniferous fossil, a 

 species of ortlwceras, too imperfect for the identification of 

 the species, but closely resembling the one figured below (fig. 

 15), the 0. cinctum of Professor Phillips the occurrence of 

 which in this locality is strongly in favour of the view already 

 advanced (Arts. 8, 24) regarding the age of these sandstones. 



Fig. 15. 



It may, indeed, be urged that carboniferous fossils pass up- 

 wards into the lower portion of the Permian (lower new red) 

 system. But we submit that orthoceras is not a genus of 

 which this can be said ; a very few cephalopods, allied to 



