AKRAtf. GEOLOGY. SECONDARY STRATA. 38.9 



original state as they relate to each other. It is well 

 known that there is often a want of continuity or per- 

 sistence in strata, and more particularly in those of small 

 dimensions. In some cases they are wedge-shaped at 

 both ends, or undergo in their progress a change from 

 one substance into another. If therefore a given stratum 

 cannot always be protracted with an uniformity of cha- 

 racter for a few yards, there is no reason for assuming 

 that it ever was so protracted for miles; and the want 

 of distant correspondence in particular beds, will not 

 therefore prevent us from legitimately, concluding that 

 the general body of strata on the north side of Arran, 

 now interrupted, was once continuous. 



It has been shown that the lowermost bed at Scriden 

 is continuous, facing in two directions, and therefore 

 incurvated on a centre, and that it is followed on each 

 side of that point, by a great succession of strata increasing 

 in number as they recede from it. The whole mass of 

 strata thus following on each hand is accommodated to 

 the position and shape of the primary rocks beneath ; 

 while the edges of both sets are abruptly broken, their 

 middle portions gradually disappearing in succession 

 towards the centre and towards the fundamental bed. 

 It may therefore be safely concluded, that the outer, 

 or upper strata, now separated by a considerable interval, 

 have once formed a continuous series, of which the mid- 

 dle portions have been removed. If there is a want 

 of accurate correspondence in the details of the northern 

 and southern strata, they are still sufficiently similar in 

 their general characters to justify this conclusion. It 

 may yet be a question to which beds of this collection 

 the sandstone which forms the southern parts of Arran 

 appertains, whether to the upper or lower; and I know 

 not that any answer can be given. It is not difficult 

 to show that the unmixed red sandstone, which is found 

 in contact with the schist as far as Glen Rossie, belongs 

 to the uppermost series; since it can be .traced from 



