206 JURA. GEOLOGY. 



the one hand, and Ben shianta or Ben na caillich on 

 the other, the whole island, if the day be clear, may 

 be seen with tolerable distinctness ; and the geologist 

 will at the same time scarcely regret a labour, which, 

 independently of this advantage, will be amply repaid 

 by the extent and variety of the landscape. As the 

 principal stretch of the island lies to the northward of 

 these mountains, so the view from the northern part of 

 the group is the most interesting ; but from Ben an 

 oir a general sketch of the structure and bearings of Isla 

 will also be derived, and the ascent of this mountain 

 is therefore as necessary for the investigation of that 

 island as it is for the examination of Jura. 



To those to whom geological investigation is yet new, 

 it will not be superfluous to suggest the convenience 

 that is derived from commencing the examination of an 

 unknown country by ascending the highest places which 

 it presents. It is often from such views only, that the 

 general bearings and features of a country can be appre- 

 hended; and the geologist, who has perhaps expended 

 weeks of toil in tedious pacing about the minor details 

 of a country, often but partially exposed in the lower 

 grounds, finds his difficulties vanish in a moment on 

 viewing from the peak of some lofty mountain, the con- 

 nexions and bearings of the strata detailed as in a map. 

 This indeed is the point from which all his movements 

 should commence, and here he should form the plan 

 of his campaign; confirming, by the nearer examination 



a surface in the act of greater or less evaporation, and by the passage 

 of every cloud which impedes the radiation of heat from the surface of 

 the earth. Those who have not attended to these circumstances will 

 be surprised at the variations of temperature which it indicates when 

 ordinary thermometers are steady. I must at the same time remark 

 that there are cases where this extreme nicety would lead to inaccurate 

 results; namely, in barometrical observations, and in geodesic ope- 

 rations with chains; where a proper adaptation of the sensibilities of the 

 thermometer and of the objects to be observed, is required. 



