of the Scottish Highlands. 213 



succession, though somewhat different in structure from that in the 

 Ben Lawers section. The sericite schist of the upper argillaceous 

 zone is the highest bed seen on this mountain, being very well 

 exposed in the bold escarpment of rock forming its summit. This 

 section of the upper argillaceous series is an exceedingly interesting 

 one : besides being well seen in the escarpment of the hill, it is 

 also finely exposed in the beds of two streams that descend from 

 the broken ridge of the corrie. From the summit, which is 

 2,999 feet above sea-level, down to about the 2,000 ft. contour-line, 

 the mountain is almost entirely composed of a great series of beds 

 of finely foliated sericite schist with intercalated beds of quartzite 

 and greywacke. The sericite schist of this zone I have already 

 described ; the quartzites and grey wackes may be further noticed. 



Fig. 2. — Section across Craig Na Challeich to Loch Earn. 



b. Upper Argillaceous Zone. d. Loch Tay Limestone Zone. 



c. Middle Arenaceous Zone. e. Lower Arenaceous Zone. 



The quartzites are of an exceedingly fine texture, having been 

 highly indurated, and are plentifully charged with iron pyrites. 

 The greywackes are also of an exceedingly fine character, and 

 show some beautiful examples of lamination. The usual colour 

 is a dark greyish hue, the lamina? or banding being of a lighter 

 shade of the same colour. It is in these bands of greywackes 

 the author found traces of annelid tubes already cited. These 

 annelid tubes have undoubtedly originally been of the ordinary type, 

 being simply cylindrical tubes of sand differentiated out from the 

 surrounding matrix, and passed through the body of the worm. 

 But now, owing to the shearing and metamorphism of the rock, they 

 have been deformed into ovates, the substance of which is generally 

 lighter in colour than the surrounding rock. On weathered surfaces 

 these ovates present all the characteristics of the annelid tubes of 

 the north-west of Sutherlandshire, at times the material composing 

 the ovates being; weathered out, and showing on the surface of the 

 beds a series of cylindrical holes similar in every respect to the 

 mouth of an unaltered burrow ; at other times, the matter composing 

 the ovate being of a harder texture than the surrounding rock, they 

 stand up in buttons like the nails in a workman's boot. Seen in 

 section these burrows have all been more or less deformed from 

 their original cylindrical form, the whole of them having been 



