100 THE STRUCTURE OF THE [Ch. VI. 



two directions ; one east and west, the other north and south ; 

 and forms large rhomboidal blocks : some few groups of gra- 

 nite rocks, on the sea-shore, are split into similar blocks, which 

 have not the same direction. The granite at St. Vaast and 

 the opposite island of Tatihou is somewhat different from that 

 of Reville, though evidently in connection with it ; it is split 

 into similar blocks, and the fissures are in the same direction 

 with those at Reville ; in both places it is traversed by granite 

 veins, of which the predominant ingredient is flesh-coloured 

 felspar."* 



Similar appearances have been observed in the granitic 

 district of the east of Ireland. " In the quarries of Golden 

 Hill," says Mr. Weaver, " the granite is divided by smooth 

 parallel seams into strata, three, four, five, and more feet 

 thick, ranging north and south, and dipping E. 75. These 

 strata are sometimes, though rarely, intersected by cross joints, 

 under an oblique angle, which are mostly parallel to each 

 other : in such cases each stratum becomes naturally separated 

 into tabular or columnar masses of a rhomboidal form." " In 

 Glencullen, the granite is also divided into great massive 

 strata, which range 20 east of north and west of south, and 

 dip into the mountain to the westward, at an angle of 70. 

 And on the Dalkey coast, a large insulated granite rock, in its 

 natural position, is composed of parallel layers from one foot 

 and a half, to three feet and a half thick, ranging north and 

 south, and dipping 70 east."f The numerous instances on 

 record, of the stratification of granite, are of the same nature, 

 the mass being divided by seams into regular beds: thus, 

 " the granite on the French coast, near the mouth of the 

 Loire, exhibits this appearance of stratification; the beds 

 running S. E. and N. W., dipping towards the S. W., under 

 the sea, at a moderate angle of inclination." f 



From these facts we arrive at the important conclusion, 

 that the granitic rocks are not rude and shapeless masses, as 



* Geol. Trans. (New Series), vol. i. p. 87. 



t Geol. Trans., vol. v. p. 138. J Annales des Mines, tome iv. p. 25. 



