302 GENERAL COMPARISON OF 



found in cases where such strata can be traced in a 

 continuous direction. Whatever these variations may 

 be, they can all be resolved into changes of the thickness 

 of the strata ; in consequence of which, while some are 

 attenuated, or even worn out in their courses, others in- 

 crease in their dimensions. 



In contemplating these alternations there is nothing 

 more remarkable than the frequent change of substance, 

 and the tenuity of the strata which are thus intermingled 

 with each other; a change, not as in Seil or Shuna, 

 confined to a small space, but extending from one end 

 of the series to the other ; from the eastern side of Gigha 

 to the western border of Isla. It has already been seen 

 that in consequence of this perpetual change, substances, 

 generally considered as occupying distinct places on the 

 surface of the earth in a regularly consecutive order, are 

 here repeated without any distinction of priority or pos- 

 teriority ; clay slate for example being sometimes found 

 above and sometimes below micaceous schist ; sup- 

 posed anomalies concerning which I need here add 

 nothing, as they have been frequently pointed out in 

 the descriptions of the several islands. 



It is further interesting to compare the strata which, 

 though found in different islands and at a considerable 

 distance from each other on the line of bearing, appear 

 to be only detached portions of one mass, the intermediate 

 parts of which are concealed by the sea that divides 

 them. Between Lunga, Scarba, Jura, and Isla, the 

 continuity is so little interrupted and the resemblance 

 so perfect, that there can be no hesitation in thus uniting 

 them; while a similar identity will be found in Luing, 

 Torsa, Seil, and Kerrera. It is less easy to trace some 

 of the resemblances next to be pointed out, in consequence 

 of their wider separation ; but it is at the same time more 

 interesting, as it explains the connexions of strata, the 

 partial occurrence of which would otherwise make them 

 appear as irregularities in a series in other respects very 



