180 Dr. Mac Culloch's Supplement to the 



tending to remove. Repeated and careful examination of them 

 as they occur in the western islands, have, since the time at which 

 the original paper on Sky was drawn up, enabled me considerably 

 to amend their history, and to dispose of them in a more exact 

 and connected manner ; but as the detail would here be inadmissi- 

 ble, from the length of discussion to which it would lead, I shall 

 make no attempt to improve the former imperfect remarks, but re- 

 serve that which might be here added, for some future communi- 

 cation. I shall however attempt to amend one or two of the des- 

 criptions contained in the former paper, where I had been obliged 

 to rely on a distant view, and was therefore compelled to speak 

 only in the most general terms. 



The first of these portions of trap is that which occupies the 

 district of Trotternish, of which, as well as of the stratified sub- 

 stances but just described, I had formerly an opportunity of form- 

 ing only a very superficial notion. 



As I have just shewn, it both intersects and surmounts the se- 

 condary strata, while in many places it appears also to be horizon- 

 tally or conformably interstratified with them. These interferences 

 are very remarkable, and exhibited on a scale of such extent as to 

 include every circumstance which has yet been described on the 

 subject of their junctions. But without numerous drawings no 

 adequate idea of them can be conveyed, and as there is little to be 

 said respecting them which would not be a repetition of the remarks 

 which have on numerous occasions been made on similar appear- 

 ances, I shall forbear to enter into details respecting them. I 

 shall only observe, that all these irregularities occur in a mass, 

 which taken in a general view, has the character of a strati- 

 fied trap, since notwithstanding them it bears a strong parallelism 

 to the already parallel strata with which it is associated. It is abun- 



