88 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 894, 



overlying ' Pipe-rock,' based on the peculiar features of the vertical 

 burrows in the quartzite, are also found to hold good, having been 

 traced even south of Loch Maree. In the third sub-zone Sallerella 

 has been noted on Ben Arkle (Sutherland) in a massive quartzite 

 free from vertical worm-burrows, and a similar band without the 

 ' serpulite ' has been noticed in the Loch Maree district. 



We now come to the details of the discovery of Olenellus. The 

 ' Fucoid '-beds, it would seem, preserve their character as brown 

 dolomitic shales with bands of rusty dolomite ; and it is in the 

 upper portion of this series that fragments of this early trilobite 

 were first found. A mountain-stream has cut a natural section, 

 and the attention of the observer, we are told, is at once arrested 

 by two prominent bands of dark blue shale, intercalated in the 

 normal dolomitic beds of the zone. The upper band is about 3 feet 

 and the lower one about 9 feet from the top of the ' Fucoid '-beds, 

 and it was in the lower band that the fragments were found, the 

 best specimens being confined to a seam less than an inch thick. 

 It would also appear that dark blue shales, near the top of the 

 ' Fucoid '-beds, have been observed in various localities, evidently 

 occupying the same horizon as the Ole7iellus-shales in the Dundonnell 

 Forest. The Authors were sanguine at the time that these shales 

 would be traced continuously through a great part of Ross-shire. 

 The locality where the trilobites were found in the zone of the 

 ' Serpulite '-grit is about 8 miles N.N.E. of Loch Maree. At this 

 spot a small escarpment gives a full section of the zone, here 

 about 36 feet thick, consisting of quartzite and quartzose grits with 

 a little shaly matter here and there, especially in the lower half. 

 In a hand of dark blue shale in the lower part of this formation a 

 head-shield and other fragments of Olenellus were found, the species 

 being apparently the same (0. Lcrpworthi) as that occurring in the 

 ' Fucoid '-beds. 



Of the organic remains obtained from the dark shale-bands frag- 

 ments of trilobites are the most abundant, but with these are 

 associated the remains of pteropods,iamong which a Solterella like 

 S. pulchella occurs. Several species of Hyolithes also are found, 

 besides one specimen of a large entomostracan. The association of 

 Saltcrella with Olenellus, say Messrs. Peach and Home, induces a 

 hope that traces of this trilobite may be found wherever the ' Serpu- 

 lite ' has been shown to abound, possibly even in the lowest group of 

 limestone. After these discoveries it could no longer be doubted that 

 the Quartzite, ' Fucoid '-beds, and ' Serpulite '-grit belong to a very 



