312 Dr. Mac Culloch on the Geology of Glen Tilt. 



quartz rock, and we have also seen that the calcareous beds them- 

 selves alternate with beds equally continuous of quartz rock and of 

 schist. We have seen that the great mass of quartz rock is followed 

 by a small bed of limestone, and that this again is succeeded by mi- 

 caceous and clay slate, terminating the series of the bedded rocks in 

 this direction. Here then is an order of rocks different from that 

 which we are taught to believe universal, since the micaceous schist 

 is far removed from the granite, and only follows a succession of 

 limestone and quartz rock. It is the limestone which immediately 

 follows the granite, and that granite is probably a portion of the 

 great mass which forms the central granite of Scotland. 



This contact of the limestone and granite is- too well marked to 

 admit of dispute, however, like many of the other remarkable cir- 

 cumstances attending on Glen Tilt it has been overlooked. 



But there are other important phenomena which accompany 

 the junction of the limestone with the granite. Recurring to the 

 alternations between the limestone and the beds of schist and 

 quartz rock with which it is continuous, we find that these alterna- 

 tions are regular, even, and defined. But if we now trace down- 

 wards to the granite, we do not find any one of these beds conti- 

 nuously in contact with the granite ; on the contrary it is some- 

 times the schist, sometimes the quartz rock, sometimes the lime- 

 stone, or there is a want of conformity between the granite and the 

 rocks which lie above it. This is not the appearance which we 

 ought to expect had the superincumbent strata been deposited on 

 the previous basis of granite. If the granite had been the lowest of 

 a series of deposited rocks and the basis on which the incumbent 

 ones were precipitated or crystallized, all the strata, which lie on it 

 should have followed upwards from it in a regular order of succes- 

 sion. That rock which was contiguous to the granite in one place 



