32 Dr. Mac Culloch's Sketch of the 



filate and quartz rock as unstratified, but their want of regularity irt 

 the present instance, compared with the extreme precision and 

 ■order of those which follow, render the distinction convenient here 

 for the temporary purpose of describing them. I have in other 

 instances produced sufficient examples of the alternate and regular 

 stratification of quartz rock and mica slate to render it unnecessary 

 to say more on that subject : I have in the same places shown that 

 -these rocks alternate with clay slate, and my object at this moment 

 is to distinguish strongly the sudden change from great disturbance 

 to extreme regularity, which takes place here between two rocks 

 which in so many other instances seem to have undergone together 

 the common action of some disturbing force. 



The first of these rocks is a compound series of beds consisting 

 of dark blue quartz rock interlaminated with thin layers of clay 

 slate of the same colour : these are to be found in immediate con- 

 tact with the white quartz rock, and in an order which Is conform- 

 able to the general position of that substance where it is in contact 

 with them. Often the quartz of this rock prevails to the total exclu- 

 sion of the schist, and the beds are then much thicker than when the 

 chist interferes. They hold a remarkably even and straight course 

 for a considerable space on the north side of Loch Eishort, dipping 

 to the N.W. at an angle of about 30°. The thickness of this set 

 of beds appears to be extremely variable, but I know not that it can 

 be ascertained, since the excavation which forms Loch Eishort in- 

 terferes with the observation at the western point of their exposure, 

 as the sea In that place covers the elevated edges, while in their 

 <:ourse eastward they become clothed with the covering of soil. 



There is consequently a chasm in my attempt to trace their 

 extent eastward, but as the same rock appears on the eastern side 

 ^with all the same characters, and in the sanie position with respect 



