340 SKY. GEOLOGY. SECONDARY STRATA. 



combined with their partial scattered occurrence and 

 the absence of points for geographic reference, it would 

 be useless, if it were practicable, to give a topographic 

 detail of the places where they occur, as these could 

 not be verified by subsequent observers. For the same 

 reasons it is impossible to represent parts so minute 

 in a map, however large its dimensions ; and I have 

 therefore been obliged to lay down the whole surface 

 as consisting of trap, even in those places where the 

 inferior strata come distinctly to light. They are in- 

 dicated on the shore alone by a continuous exterior line 

 of colour; even there incapable of being so varied as 

 to distinguish the calcareous from the sandstone beds, 

 and intended only to mark their boundaries on the sea line. 

 The examination of the surface of the country is 

 not the less necessary ; since, while it is required for 

 determining the continuity of the strata, it serves, together 

 with the altitudes of the eastern cliffs, to ascertain their 

 thickness ; or at least to assist us in forming a tolerable 

 conjecture respecting that circumstance. If we imagine 

 the whole of Trotternish divested of its mountainous 

 irregularities, it can be reduced to a sort of inclined 

 'table land, of which the highest elevation will be found 

 between Portree and Holme, and the lowest between 

 Loch Uig and Duin. Wherever the land is so low 

 as to coincide with this table, the strata are seen; 

 subject however to the usual irregularities that arise 

 from intervening and intersecting trap ; and it will 

 be found that their dip, which is to the north-west, 

 conforms to this imaginary level. It is for this reason 

 that they are thickest between Portree and Holme, 

 where they form cliffs of five or six hundred feet in 

 elevation ; while towards Eilan Fladda northward, and 

 Kilmuir eastward, they occupy low situations on the 

 shore. It is thus evident, that the basis of Trotternish 

 is a set of inclined strata, elevated and consequently visible 

 on the east coa&t, but dipping to the north-west so as 



