Geological Society of London. ' 137 



deposits, whilst material corresjDonding to the ' Head ' seals up the 

 cave-mouths. The ossiferous breccias of the caves are therefore 

 intermediate in age between the beaches and the ' Head.' 



The origin of the boulders is discussed, and it is inferred that they 

 have been brought, not from the French coast, nor from a submerged 

 land, but from a north-easterly source by floating ice through the 

 Straits of Dover. The mollusca of the Eaised Beaches, of which 

 a list of 64: is given, are closely related to forms living in the 

 neighbouring seas. 



These Eaised Beaches are not of the age of the Higher Valley- 

 gravels ; but the evidence (especially that yielded by the Somme 

 Valley deposits) points rather to their connexion with the Lower 

 Valley-gravels, and therefore, with the exception of the Caves, they 

 represent the latest phase of the Glacial Period. 



2. " The Olenellus-Zone in the North- West Highlands." By B. N. 

 Peach, Esq., F.E.S.E., F.G.S., and J. Horue, Esq., F.E.S.E., F.G.S. 

 (Communicated by permission of the Director-General of the Geologi- 

 cal Survey.) 



In the stratigraphical portion of this paper brief descriptions are 

 given of certain sections in the Dundonnell Forest, from eight to 

 ten miles N.N.E. of Loch Maree, which, have yielded fragments 

 of Olenellus. The organisms are embedded in dark-blue shales 

 occurring near the top of the 'Fucoid Beds' and towards the base 

 of the ' Serpulite Grit,' forming part of the belt of fossiliferous 

 strata stretching continuously from Loch Eriboll to Strome Ferry — 

 a distance of ninety miles. 



In the Dundonnell Forest the basal quartzites rest with a marked 

 unconformability on the Torridon Sandstone. There is an unbroken 

 sequence in certain sections from the base of the quartzites either to 

 the ' Serpulite Grit ' or to the lowest bands of the Durness Lime- 

 stone. At these horizons the strata are truncated by a powerful 

 thrust, which, at Loch Nid, brings forward a slice of Archaean rocks 

 with the Torridon Sandstone and basal quartzite. 



The strata from the base of the quartzites to the base of the 

 Durness Limestone, exposed in the Dundonnell Forest, are compared 

 with their prolongations to the north and south of that region, from 

 which it appears that there is a remarkable persistence of the various 

 subzoues identified in Assynt and at Loch Eriboll. But between 

 Little Loch Broom and Loch Kishorn dark-blue shales near the 

 to}:) of the ' Fucoid Beds ' have been observed at various localities, 

 ■evidently occupying the same horizon as the Olenellus-sheLles in the 

 Dundonnell Forest. 



The Serpulites (Salterella) associated with the Trilobites in the 

 ' Serpulite Grit' occur in the basal bands of the overlying limestone; 

 they were found during last season in the brown dolomitic shales 

 accompanying the Olenellus-s\mles in the ' Fucoid Beds,' and they 

 were formerly detected in the third subzone of the ' pipe-rock ' in 

 Sutherland. Their appearance on these horizons leads us to cherish 

 the hope that portions of Olenellus may yet be met with in certain 

 'shales in the quartzites and probably in the lowest group of limestone. 



