Geology of the South-east of Devonshire. 



479 



recent than the new red sandstone, and that of Brora, than the oolites. On the 

 Continent, the observations of Elie de Beaumont*, Hugif, Studer J, and Dufrenoy§, 

 show that in the Oisans, Bernese Alps, and Pyrenees, the central axes of granite 

 must have been in a fluid state since the cretaceous period. In no part of the 

 world can any granitic mass be proved to be of great antiquity, — an ancient funda- 

 mental rock ; the masses which are now in contact with any of the palaeozoic strata 

 are all intrusive ; and the granitic eruptions of the S.W, of England may be per- 

 haps added to the proofs, already numerous, that this particular crystalline form 

 was most extensively projected at the close of the secondary period, and caused 

 or accompanied that contrasting condition of surface which the subsequent tertiary 

 period must have presented. 



Important changes have resulted in Devonshire from the intrusion of so many 

 heated masses among sedimentary rocks, and some of these have been already no- 

 ticed. The greenstone trap of Holbeam, Denbury, &c., very constantly obliterates 

 the lines of deposition or cleavage of the slates. Fig. 16. represents a case to be 

 seen in a quarry near Ogwell, where a great mass of trap would appear to have im- 

 parted diagonal lines to the slate. With the assistance of map, PI. XLII., all the 



Fig. 16. 



Slate with oblique structure resting on trap near Ogwell. 



various intrusive masses of trap will be so easily found by the field geologist, and 

 the effects they have produced are so obvious at each locality, that any description 

 in addition to what has already been incidentally given in other places, is not 

 required. 



Nor are less important changes exhibited in the neighbourhood of the granite : 

 carbonaceous shales are converted into black slate ; arenaceous beds become mica- 



* Faits pour servir a I'Histoire des Montagues de I'Oisans, Mem. Soc. Hist. Nat. de Paris, tome v. 

 Memoire pour servir Desc. Geol. de France, torn. ii. ; also Dausse sur la forme, &c., de la chaine des 

 Rousses, Mem. Soc. Geol. de France, tome ii. p. 125, 1837. 



t Alpen Reise. 



X Bulletin Soc.Geol.de France, tomeii. p. 51 etseq.,1831 ; also Carte Geologique des Chaines entre 

 les lacs de Thun et de Lucerne, Mem, Soc. Geol. de France, tome iii.p. 379, 1839. 



§ Mem. pour servir Desc. Geolog. de la France, tome ii. 



3q2 



