Dr. Mac Culloch on the Geology of Glen Tilt. 313 



should have been contiguous to it every where, since this law is in- 

 variably found to hold good among rocks of which the stratification' 

 is demonstrated. This observation is of importance, and I have 

 illustrated it by two sections, the one showing the fact as it ac- 

 tually exists, and the other the order which should take place had 

 the strata been regularly deposited on the granite.* In addition to 

 the irregularity of this line of contact, symptoms of confusion and 

 disturbance are apparent, "f in every instance where the granite is 

 actually visible in contact v;irh the neighbouring rocks. These 

 consist in a general mixture of all the stratified rocks with the 

 granite, and a total discomposure of their regularity, being at the 

 same time accompanied by the passage of minute veins from the 

 mass of granite into the stratified recks. Where on the contrary 

 the beds lie out of the immediate viclnit}^ of the granite, they retain 

 their parallelism and regularity, its influence appearing to extend 

 to a very short distance beyond the point of actual contact. 



The real structure of Glen Tilt, and the true cause of the ap- 

 peal ances which have excited so much notice, must now be seen 

 so clearly to follow from the history of the rocks which bound ir, 

 that it is almost superfluous to give a summary view of the whole. 

 I will however conclude this account with such a sketch, illus- 

 trating it by a map and such sections as may render the whole 

 more obvious to those who may be inclined to follow me over the 

 same tract.J The map does not pretend to minute accuracy with 

 respect to every rock over this large space. It would have been in 

 fact impossible to have laid down such details on a survey of this 

 nature, the only one which has yet been executed of this district. § 



* Plate 21, fig. 2 & 3. + Vide Plates 14, 15, 16, 17, 18, & 20 fig. 4. 



X Vide Plates 13 & 20. 

 § I am indebted for this Map to the Duke of AthoU, it being the survey of part of hi* 

 estate, and executed by Stobie, the author of the General Map of Perthshire. 



Vol. jii, 2 r 



