86 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 894, 



accumulation, affording time for the fertilization of the sand by the 

 shower of minute pelagic organisms. Truly this was the age of 

 worms, that continued masters of the situation through the period 

 represented by the ' Fucoid '-beds. The ' Serpulite '-grit is evidence 

 of coarser sediment, but after its deposition hardly any material 

 derived from the land entered into the composition of the overlying 

 limestones. Eventually, he continues, nothing seems to have fallen 

 on the sea-floor but the remains of minute organisms, whose calca- 

 reous and siliceous skeletons have slowly built up the great mass of 

 limestone and chert so conspicuously developed at Durness. Worms 

 were still in the ascendant, since most of the beds are traversed by 

 worm-casts in such a manner that nearly every particle must have 

 passed through their intestines. Indeed, he considers that the 

 prevalence of these annelid-traces indicates that the limestones 

 cannot be due to coral-reefs. Moreover, only one undoubted speci- 

 men of a coral, resembling a Michelinia, has been observed. Neither 

 had shell-banks much to do with the accumulation of the limestone, 

 as may be seen from the mode in which the shells occur. The most 

 abundant forms are chambered shells, such as Nautilus, Lituites, and 

 genera of the Orthoceratidae. Next in order are the gasteropods, 

 chiefly Maclurea (heteropod), and Pleurotomaria, whilst the lamelli- 

 branchs and brachiopods rank last in point of numbers. Sponges 

 of the genera Archceocyathus and Calaihium occur at intervals in the 

 muddy matrix. However, the larger masses of chert in the lime- 

 stone do not seem to be derived from sponges, but more probably 

 from the siliceous skeletons of diatoms. No undoubted remains of 

 foraminifera have been discovered, and he thinks it unlikely that 

 minute organisms would be preserved, owing to the fact that the lime- 

 stones are crystalline and that many of them are more or less 

 ' dolomitized.' This latter word is the only one to which I would 

 take exception. If we substitute ' dolomitic,' it will leave open the 

 question of origin, which I think may be important in this case. 



Mr. Peach endorses the views of Salter that the fossils are of an 

 American type. So far as the order of succession of the beds is 

 concerned, we have, he says, an almost exact counterpart of the 

 strata exposed along the axis of older Palaeozoic rocks, stretching 

 from Canada through the Eastern States of the Union. His 

 inferential correlation of the ' Pipe-rock ' of Sutherland with the 

 Potsdam Sandstone, based on the prevalence of Scolithus, will 

 scarcely hold good in view of the later researches of the Survey. 

 The correlation of the Durness Limestone with the ' Calciferous 



