230 MESSRS. PEACH AND HORNE ON" THE 



Sandstone is truncated by the Moine Thrust which ushers in the 

 Eastern Schists. 



§ 4. Sections north of Allt Eigh Ian. 



Immediately to the north of Allt Righ Ian the strata between 

 the higher zones of the ' Pipe-Eock ' and the basal bands of the 

 Durness Limestone are admirably displayed in several important 

 stream-sections. They are of special interest from the excellent 

 exposures of the Olenellus shales and from the organisms found in 

 the dolomitic bands associated with the dark blue shales. No 

 fragments of trilobites have as yet been found in these sections, 

 partly owing to the difficulty of following the fossiliferous layer 

 along the line of outcrop. 



One of these streams (unnamed on the six-inch map) rises on the 

 moory watershed between Allt Coire Chaorachain (draining into 

 Strath Beg) and Strath na Sheallag. About a mile to the north of 

 Allt Eigh Ian it is crossed by the hill-road leading to Dundonnell, 

 whence it flows southwards for g mile, where it is joined by a small 

 tributary (Allt a Chip). Here the main stream is deHected to the 

 south-west, joining the Loch an Nid river near the mouth of Allt 

 Eigh Ian. 



Ascending Allt a Chip from the point of junction with the main 

 stream, where the lowest sub-zone of the ' Pipe-Eook ' is seen resting 

 on the basal quartzites, ah excellent section is exposed in the sides 

 of a small gorge. The various sub-zones of the ' Pipe-Eock ' are 

 overlain by the ' Pucoid Beds,' the two bands of dark blue shale 

 occupying their respective horizons near the top of the zone and 

 separated by the normal dolomitic beds. Here their thickness can 

 be accurately measured on the sides of the chasm ; that of the 

 upper being 3 feet and the lower 19 inches. A layer of rusty 

 dolomite about a foot thick, overlying the lower band of dark 

 blue shale, was found to be crowded with excellent specimens of 

 Hyolitlies, sp. 



Eeturning to the main stream of which Allt a Chip is an affluent, 

 the observer crosses a similar succession of strata as he follows the 

 section towards the watershed. Here again both layers of dark blue 

 shales are visible near the top of the ' Pucoid Beds,' the upper one 

 cropping out at the base of a small waterfall formed by the overlying 

 ' Serpulite Grit.' A few yards below this latter locality numerous 

 serpulites (Salterella) were observed in a brown dolomitic band 

 associated with the Olenellus shales. Crossing the ' Serpulite Grit ' 

 there is an excellent exposure of the basal bands of the overlying 

 Durness Limestone, forming a prominent cliff on the east bank of 

 the stream about 300 yards to the south of the point where it is 

 traversed by the hill-road leading to Dundonnell. Here the top of 

 the ' Serpulite Grit ' passes below black shaly limestone, 4 feet in 

 thickness, succeeded by 15 feet of dark mottled limestone. The 

 black limestone-shales, weathering with a brown tint, are slightly 

 cleaved, but they are crowded with splendidly-preserved specimens 



