234 MESSES. PEACH AISTD HOENE ON THE 



one of US observed along the crest of the ridge between Sgurr Ban 

 and Ben a Chlaidheimh, on the west side of the Loch an Nid valley, 

 vertical worm-casts in a band of quartzite belonging to this zone. 

 In the Ben Eay Porest, south of Loch Maree, certain dark grey shales,- 

 which may probably yield organic remains at some future time, 

 occur near the base of the series. 



The overlying zone of* Pipe-Eock,' from 250 to 300 feet thick, dis- 

 plays in the Dundonnell Forest the five sub-zones so typical of this 

 subdivision in Assynt and the regions northwards .to Loch Eriboll.^ 

 They have been traced southwards through the mountainous region 

 south of Loch Maree towards Loch Kishorn. The sub-zones are based 

 on the peculiar features of the vertical burrows in the quartzite^ 

 which are probably due to different species of errant annelids. 



At the top of the third sub-zone on Ben Arkle, Sutherlandshire, 

 numerous examples of Se^-joulites Maccullocliii {Sdlterella) were 

 observed in massive quartzite free from the vertical worm-burrows. 

 A band possessing the same lithological characters, and occupying 

 the same relative position, has been noted in certain sections in 

 Assynt and to the south of Loch Maree, but hitherto it has yielded 

 no serpulites. 



The ' Fucoid Beds,' varying from 50 to 80 feet in thickness, are 

 remarkably uniform in character when traced along the belt south- 

 wards from Loch EriboU. Consisting mainly of brown dolomitic shales 

 with bands of rusty dolomite, they are traversed by numerous worm- 

 casts, usually flattened and resembling fucoidal impressions, a re- 

 semblance which misled the older observers. But between Little Loch 

 Broom and Loch Kishorn dark blue shales near the top of the zone 

 have been observed at various localities evidently occupying the 

 same horizon as the Olenellus Shales in the Dundonnell Porest. 

 Our colleague, Mr. Gunn, has traced these dark blue shales across 

 the col from Strath na Sheallag into AUt Gleann Chaorachain, towards 

 Strath Beg. They have been observed in Glen Logan, near Kin- 

 lochewe, and on Meall Giubhais to the south of Loch Maree. 

 Another officer of the Geological Survey, Mr. Lionel Hinxman, has 

 also detected them at the top of the * Eucoid Beds,' in the thrust- 

 area that occupies the pass between Glen Kishorn and Tulloch 

 in Strath Carron. It is not improbable that the Olenellus Shales 

 may yet be traced continuously through a great part of Eoss-shire. 



Of special interest is the occurrence of Serpulites Maccullochii 

 (Salterella) and Hyolithes, in fine preservation, in brown dolomitic 

 bands associated witli the Olenellus Shales near the top of this zone. 



Along the boundary-line between the ' Eucoid Beds ' and the over- 

 lying zone of ' Serpulite Grit,' from 25 to 40 feet thick, there is fre- 

 quently an alternation of false-bedded grits and shales, evidently the 

 passage-beds from the one horizon to the other. This intermediate 

 series is conspicuously developed in the Loch Eriboll region, and it 

 has been observed to a more limited extent in Eoss-shire. 'Near the 

 crest of the zone the quartzites merge into carious dolomitic grit 



1 See Quart. Journ. Geol. Soc. vol. xliv. (1888). p. 406. 



