412 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 16, 



of quartz and felspar grains. The lower beds are more porous, 

 and consist of a brownish red felsite basis, with nodules of a soft 

 white mineral, like Bole. Similar red strata are seen at many points 

 on this side of the peninsula, and often with such a mixture of cha- 

 racters as to render it difficult to decide whether they should be classed 

 with igneous or aqueous formations. Indeed it seems probable that 

 they may so far partake of the nature of both, being in great part com- 

 posed of the volcanic detritus thrown out during the formation of the 

 felspar porphyries, and thus of the same nature with the " volcanic 

 grits " of Sir R. Murchison, and some of the " ash-beds " of Sir H. 

 De la Beche and the Geological Survey. The want of a good phy- 

 sical map on which to record my observations, and of time to work 

 out detailed sections, renders me still doubtful whether the connec- 

 tion of these beds with the red conglomerates is more than incidental. 

 They may not improbably form a distinct and more recent group. 



The next group of strata we shall notice is the Coal- formation, 

 which occurs on the west side of the peninsula near Machrihanish 

 Bay. Coal has been long wrought in the low valley or Laggan west 

 of Campbeltown, but the beds appear to be now nearly exhausted, 

 and the coal generally of inferior quality. The plants found both in 

 the coal itself and in the connected shales, leave no doubt that these 

 beds belong to the true Coal-formation, and not to the Lias as is often 

 said. Fine specimens of the Stigmaria ficoides are common not only 

 in the shales but in the coal itself, some beds of which seem chiefly 

 formed of this plant and of a species of Calamites. Lepidodendra 

 abound in the shales and sandstones, along with Lepidostrobi. The 

 only Fern seems a Pecopteris, but in general only the stalks are left 

 without any of the leaflets attached. Branches of Stigmaria, slightly 

 compressed, and filled, in some instances, with iron-pyrites, in others, 

 with a conglomerate of coarse grains of quartz in a basis of iron- 

 pyrites, also occur in the coal. In some of the sandstones in Tir- 

 fergus Burn grass-like impressions and fragments of small stems 

 occur, but too imperfect for the determination of their true cha- 

 racters. 



The best section of the carboniferous strata is exhibited in the 

 banks of the stream just named, which runs as it were in a kind of 

 notch cut in the declivity of the hills forming the south side of the 

 Laggan. The stream rises in the trap forming the hills towards 

 Losset. In descending the ravine, the first strata observed are some 

 coarse red conglomerates, consisting chiefly of trap-boulders. On 

 these rest deep red ochrey shales, all dipping east down the stream. 

 After a short interval, in which the rocks are concealed by herbage, 

 deep red shales, apparently the continuation of the former beds, 

 form the bank of the stream. The section is again concealed for 

 some yards by grass, but is resumed by a mass, about 40 feet 

 thick, of shales, purplish or greyish brown below, and passing up- 

 wards through bluish grey and reddish white beds, into deep black 

 shale above (see fig. 1). These gradual changes of colour in the 

 strata as we recede from the igneous rock mark in a very beautiful 

 manner the gradual diminution of its metamorphic influence as the 



