NTCOL SOUTHERN GRAMPIANS. 189 



50° N. 40° W., in fine granular mica-slate. Still lower, I found 

 a thick bed of clay-slate, reticulated with numerous veins of quartz, 

 similar to one mentioned in the section on the east bank of the Lub- 

 naig ; and some slate-quarries are wrought high up on the hill, but 

 probably lower in the series. Further south, and quite within the 

 gorge of the river, a concretionary red felspar-porphyry appears, 

 similar to the porphyry at the Leny lime-quarry. Below it there is 

 a red greywacke, followed to the south by other beds, apparently the 

 mere continuation of the first beds in the former section, but much 

 concealed by woods and detritus. 



9. General Remarks on the foregoing Sections. — I have given fuller, 

 perhaps it may be deemed tedious, details of the changes in character 

 and in dip and direction of these strata than might otherwise have 

 been necessary, from the great theoretical importance of this section. 

 A mere casual walk along the road, with its numerous turnings and 

 windings, and the distraction occasioned by the wild and romantic 

 scenery, is apt to leave on the mind an impression of greater regu- 

 larity in the sequence than really exists. And so it is when the 

 facts are at once generalized, the numerous exceptions ignored and 

 passed over, and mere averages, deduced or assumed, only stated. 

 In such a method of procedure both author and reader are deceived, 

 and a regularity imagined which has no existence. I have felt this 

 to be the case in reference to these sections. The first general im- 

 pression is, that there is here a continuous series of beds dipping 

 regularly to the north, one below the other. In that case the grey- 

 wacke to the south would be the lowest and oldest deposit, followed 

 first by clay-slate, and this by mica-slate, as the upper and newest-for- 

 mation. This is, of course, exactly the opposite order from that noted 

 in the former sections, and cannot therefore be adopted without some 

 consideration. To the general question of order I shall subsequently 

 advert, and would now only direct attention to one or two special 

 points. The first of these is the marks of disturbance in the sections, 

 indicated both by igneous intrusion and by changes in the dip and 

 direction of the beds. This is especially seen in the Leny section, 

 fig. 3, at the points marked A and B. The beds north and south of 

 A seem merely the same group repeated. At B a more decided 

 change takes place, and here Dr. Macculloch has drawn the line of 

 junction between the clay-slate and mica-slate. Clay-slate indeed 

 occurs north on Loch Lubnaig, but more talcose and foliated, or cry- 

 stalline, than the strata south of B. In Ben Ledi, also, beds con- 

 taining distinct fragments run far into the interior. The two sets of 

 division-planes seen in Ben Ledi give rise to another important 

 question, — which of these indicates the true bedding or stratification ? 

 If the lines of foliation in the slates are not truly lines of bedding or 

 deposition, and we must look for these in the other set of division- 

 planes, then the whole order of the formations is reversed. It would 

 undoubtedly be easier to assume either supposition as true, than to 

 assign a sufficient reason for the choice made. 



10. Comrie and Strath Earn. — The next locality I have to notice 

 is Upper Strath Earn, near Comrie, again about twelve miles north- 



