ii Early Observations on Basalt 55 



sent to the Boyal Society a letter he had received from 

 E. Mendez da Costa telling him that " in Cana Island to 

 the southward of Skye and near the island of Kum the 

 rocks rise into polygon pillars . . . jointed exactly like 

 those of the Giant's Causeway." x But it was reserved for 

 Sir Joseph Banks to give the first detailed account of the 

 cliffs of Staffa and Fingal's Cave, which from that time 

 shared with the Giant's Causeway in the renown that 

 drew a yearly increasing number of travellers to these dis- 

 tant shores. 2 



Much had thus been learnt as to the diffusion of basalt 

 in Europe, and many excellent drawings had been pub- 

 lished of the remarkable prismatic structure of this rock. 

 But no serious attempt seems to have been made to 

 grapple with the problem of its origin. Some absurd 

 notions had indeed been entertained on this subject. The 

 long regular pillars of basalt, it was gravely suggested, were 

 jointed bamboos of a former period, which had somehow 

 been converted into stone. The similarity of the prisms 

 to those of certain minerals led some mineralogists to regard 

 basalt as a kind of schorl, which had taken its geometrical 

 forms in the process of crystallization. Kome' de Lisle is 

 even said to have maintained that each basalt prism ought 

 to have a pyramidal termination, like the schorls and other 

 small crystals of the same nature. 3 



Guettard, as we have seen, drew a distinction between 



1 Phil. Trans. Hi. (1761) p. 163. 



2 See Pennant's Tour in Scotland, 1772, where Banks's narrative is in- 

 serted with a number of excellent engravings of the more remarkable features 

 in Staffa. 



3 In the second edition of his Crystallographie (1783) he clearly dis- 

 tinguishes between crystallization and basaltic structure. The latter he 

 regards as due to desiccation or cooling, tome i. p. 439. 



