36 ■ Dr. Mac Culloch's Sketch of the 



length in other places the errors that may arise in these observations, 

 and need not enter largely into the question in this place, but it 

 appears to me a sufficient argument that two sets of rocks are not 

 consecutive if those which correspond in one place do not also corre- 

 spond throughout. I should expect to find that the same bed of 

 red sandstone exists between Kyleaken and Broadford, where I had 

 no opportunity of looking for it ; but beyond that it is not likely to 

 occur, as the limestone which lies at some distance above it in the 

 order of superposition occupies the lowest situation on the shores of 

 Broadford. I mentioned that the same bed is to be found at Loch 

 Scavlg, where it is plainly connected with the very large mass of simi- 

 lar sandstone which constitutes the main part if not the whole of the 

 island of Soa ; it occupies here the lowest visible situation, being 

 washed by th^ sea and exposing but an inconsiderable thickness, 

 since it is shortly followed by the trap, when it finally disappears, 

 none of the subsequent stratified rocks which accompany and follow 

 it near Loch Eishort being here found. It is here interstratified 

 with beds of a schist which has sometimes the character of fine clay 

 slate, while at other times, the laminse being separated by coarser 

 particles of sand and of mica, it puts on the character of that which 

 has been called fine graywacke slate. I have on other occasions 

 shown* that these rocks are not necessarily distinguished in posi- 

 tion, and that near Loch Ard in Perthshire, and Crinan in Argyle- 

 shire, the several sorts of clay slate and graywacke are irregularly 

 intermixed : the same phenomenon is to be seen in many other 

 parts of Scotland, which I cannot here pretend to enumerate ; 

 although the question is of importance to geology, this is not 

 the place in which it must be discussed. The fact abovemen- 

 tioned however extends our objections to the commonly received 



Geological Transactions, vol. 2d. 



