48 BRITISH FOSSIL CRUSTACEA. 
to the Old Red Sandstone are seen on the banks of the Nethan River, and also on those 
of other tributaries of the Clyde, particularly the Logan Water, on each of which rivers 
Mr. Slimon has marked the junction between the grey Silurian and the Old Red rocks. 
The Silurian beds rise up into several hills of considerable altitude, one of which (Nut- 
berry, 1715 feet above the sea) we ascended. Judging from the outline of the country, 
and the extensive range of similar high moorlands, I am disposed to think that these rocks 
may be found to spread north and westward over the hills of Dunside and Middlefield, 
1300 to 1500 feet high, and may even range to Cairn Table on the south, the summit of 
which, according to the 'Trigonometrical Surveyors, is 1944 feet above the sea. Advancing 
eastwards from the range of hills on the flank of Nutberry, in one part of which Mr. 
Slimon discovered an Orthoceratite, and descending the Logan Water to about a mile 
below the farmhouse of Dunside, you reach the uppermost band of the grey strata in 
which were discovered those remarkable Crustaceans which have been above referred to. 
“The lowest portions of the Silurian rocks which fell under the inspection of Prof. 
Ramsay and myself are those which are traversed by the Nethan River as it flows from 
Priest Hill and Nutberry Hill to Cumberland. Several dislocations and convolutions 
which are seen on that line among Silurian strata, as well as in the contiguous Old Red, 
are well explained by the frequent protrusion of porphyry (usually a red quartziferous 
porphyry). On the whole, however, it was manifest to both Prof. Ramsay and myself 
that m receding from the Old Red boundary, and in ascending to the higher hills by the 
course of the Nethan, we made a gathering, descending section, because the strata, suc- 
ceeding to each other with a prevalent dip to the north-east or east-north-east, consisted 
successively of differently constituted materials. ‘Thus, whilst the uppermost strata were 
dark grey and schistose, other layers of lighter colours were more siliceous and formed 
stonebands. ‘These are followed by other courses of shale and schists, in which are 
nodular concretions, occasionally calcareous, in which we looked in vain to find a few 
fossils which could have led us to suppose them (what they might very well prove to be from 
mineral aspect) the representatives of the Wenlock formation. It is from one of these 
strata that Mr. Slimon procured the Orthoceratite above alluded to, but which is too im- 
perfect to be specifically determined. With some undulations and several breaks, parti- 
cularly in the proximity of the intrusive porphyry, all these Silurian strata are inclined 
towards the east-north-east and north-east, and at angles varying from 12° and 15° to 
verticality where they roll over in flexures. 
“The inferior beds exposed in the section of the Nethan are here and there mineralized, 
and specially so where trap-rocks, chiefly greenstone, have penetrated the strata, veins of 
lead-ore and much sulphate of barytes being there apparent on the surface. 
«The section, however, which best exhibits the relations of the Silurian rocks to the 
Old Red Sandstone is seen on the banks of Logan Water, between the farms of Dunside 
and Ach Robert. The last of the decidedly dark grey and schistose beds observable in 
descending from the flanks of the Silurian hills (Nutberry, &.), are those in which all the 
