GEOLOGY OF LESMAHAGO. . ag 
fossils described by Mr. Salter’ were found by Mr. Slimon. These dark fossiliferous rocks, 
the clay-slate of mineralogists, are immediately overlain by and pass up into Red Sand- 
stone, in which there are several alternations of more or less greyish or greenish-grey 
bands, the whole, like the beds in the Nethan, dipping to the east-north-east or north- 
east. 
“ Old Red Sandstone.—In the traverse along the Logan Water I did not observe any 
unconformity between the grey beds with Crustaceans and other fossils and the overlying 
red sandstones, the lowest courses of which are marked upon Mr. Slimon’s unpublished 
map as ‘Red Silurians.’. For my own part, however, I would rather consider these red 
strata as constituting the base of the Old Red Sandstone, because they graduate up into, 
and alternate with, the pebbly conglomerates which are largely developed near Ach Robert 
and Waterside. 
«Some of the porphyries which are associated with the red rock in this part of the 
series seemed to be interstratified and of age contemporaneous with the sandstones with 
which they dip symmetrically, and like which they are jointed and exhibit the way-boards 
of sedimentary deposits. In mineral characters and in their interstratification with red 
sediments, these rocks, though of much older date, present much the aspect of some of 
the porphyries of the Rothe-todte-liegende of the Permian age in Germany. 
“The conglomerates of the Old Red of this tract differ strikingly from those of the 
same age in the North Highlands, where the so-called lower conglomerate is usually a very 
coarse breccia, the huge fragments of which are more or less angular, whilst here they 
are all worn and rounded pebbles, the largest of which scarcely ever reaches a foot in its 
greatest diameter. 
“ Most of the pebbles consist of grey and pink quartz-rock, but these are mixed with 
other varieties of crystalline and some igneous rocks. This conglomerate zone, which is 
fairly interstratified in red sandstone, and ranges from north to south (as laid down on 
Mr. Slimon’s map), is much nearer to the dark grey Silurian on the Nethan River than it 
is to the same rock on the Logan Water; whilst on the Kype Water the two rocks are 
still further removed from each other. ‘Time and detailed examination will determine 
whether this deviation of outline be due to breaks and unconformable arrangements, or 
simply to changes in the degree of inclination of the strata. By comparing the only 
watercourses which we examined, I am led to think that the difference of the angle of 
dip may sufficiently explain these diversities of superficial area, because on the Logan 
Water we found the inclination varying from 7° to 12° only on an average ; the red beds 
with imbedded porphyries and conglomerates, as well as the inferior grey beds, sloping off 
to the north-east or east-north-east at these low angles, except where they rolled over bosses 
of porphyry. On the Nethan banks, on the contrary, the beds are more highly inclined. 
1 «Quart. Journ. Geol. Soc.,’ 1856, vol. xu, p. 26. 
