186 KEPORT— 1866. 



3. The conditions of deposit seem to be, that the Harlech group was 

 nearly uniform with that of North Wales, but, being of finer grain, indicates 

 a somewhat deeper-water deposit. The Menevian, Linfjula-Jlacj , and Trema- 

 cloc rocks are all much thinner, and, as a rule, of more even deposit, than in 

 North Wales. They, too, seem to have been formed far out at sea, but pro- 

 bably in no great depth of water. 



The depression in the Arenig and Llandeilo groups seems to have been 

 greater, and particularly in contrast with the conditions of deposit in North 

 Wales and Shropshire, where shore accumulations were being everywhere 

 laid down. But in this respect they are more like the Skiddaw slates, some 

 of whose fossils they include ; and the presence of repeated beds of lava, ash, 

 and ashy slate lends no countenance to the idea that these beds were subject 

 to the oscillations of a shallow sea ; for the deposits are remarkably tranquil, 

 fine-grained, and regular. Beds of fossils occur at intervals only in the 

 Ai'enig and Llandeilo rocks, and are then plentiful, as in other deep-sea de- 

 posits. But the Tremadoc rocks, being apparently laid down on a stationary 

 sea-bed, present us with conditions wholly unlike those of the same period 

 in North Wales, and, perhaps as a consequence of this, with a very different 

 set of organic remains. 



The Harlech, Menevian, and Ffestiniog group have each large and well 

 stratified beds of true contemporaneous volcanic rock, as well as many in- 

 traded beds. j ^y SALTEK. 



HENRY HICKS. 



Report on Dredging among the Hebrides. 

 By J. GwYN Jeffreys, F.R.S. 



This exploration lasted nearly two months, viz. from the 24th of May to the 

 14th of July in the present year. It comprised Sleat Sound, Lochs Alsh, 

 Duich, Slapin, and Scavaig, and the Minch from Croulin Island to Loch Ewe. 

 I had a good cutter yacht, the master of which had been emploj'ed by me for 

 many years as dredger and took considerable interest in the work, an active 

 and willing crew, four serviceable di'edgcs, 300 fathoms of new rope, ma- 

 chinery for hauling up the ili-edges, a large tub, sieves, and various other 

 apparatus. The Hydrographer of the Navy obligingly supplied me with such 

 charts as I required, to show the depths and nature of the sea-bottom in the 

 district which I proposed to examine ; and these were of great use in dredging, 

 as well as for navigation. The weather was too fine ; we Avere often becalmed 

 for many hours together : and instead of steady breezes, we had too many of 

 those squalls which are so prevalent, and occasionally dangerous, in the He- 

 brides. 



The Hebridean seas have been often searched, but not explored, by zoolo- 

 gists. Their great extent, and the number of lochs and inlets which indent 

 the coast in every direction, would render necessary an immense deal of 

 money, time, and patience for a complete investigation. There is little pro- 

 bability that the subject of the present Report will ever be exhausted. 



The Invertebrate fauna of this district is of a northern character, although 

 there are a few exceptions. Such are, among the Mollusca, Troclms umhili- 

 caluis, Phasianella pidla, liissoa caiiceUata or cvcmdata, Odostomia lactea or 



