60 GENERAL COMPARISON OF 



spending arrangement will be necessary in drawing these 

 comparisons ; those which relate to Mull being reserved 

 to the last place. It may be added that the remote situa- 

 tion and apparently unconnected condition of St. Kilda, 

 excludes it from this general view, and that no notice is 

 taken of the smaller isles which, like Staffa, contain no 

 stratified rocks, and therefore admit of no useful compa- 

 rison. The comparison of the unstratified rocks is indeed 

 always so unsatisfactory, from the want of definite charac- 

 ters by which to judge of their relative ages and original 

 connexion, that this view must be chiefly limited to the 

 stratified substances. 



Wherever the continuity of the stratified rocks is, as in 

 this case, interrupted, any judgment respecting their iden- 

 tity must be derived, partly from the correspondences of 

 the bearings and inclinations, and partly from similarity 

 of composition. Circumstances which do not at present 

 admit of a remedy, throw an occasional shade of doubt 

 over the accuracy of the former class of observations, 

 without however destroying the evidence they are calcu- 

 lated to afford. 



The principal of these consists in the imperfections of 

 the maps on which the rocks have been unavoidably 

 delineated. These imperfections exist, not merely in the 

 outlines or dimensions of the land, but in its bearings, 

 or in the directions which the several coasts and islands 

 possess towards each other. Owing to the former, it 

 has sometimes been impossible to lay down rocks in their 

 ascertained bearings ; because, after they were deter- 

 mined, no room for them was found without falsifying 

 their positions or altering the map ; while, in many cases, 

 the erroneous positions given to the land, have led to the 

 distortion of a line of strata in the draught, where it had 

 been found in nature to be perfectly even. The most 

 remarkable of these errors have occasionally been cor- 

 rected, but they cannot be effectually removed until the 

 accomplishment of a new survey. 



