TRANSACTIONS OP THE SECTIONS. 125 



The Auchenaspis Salferi, Egerton, Is a remarkable little Cephalaspidian fish, which 

 has hitherto been detected only in the grey passage beds of Ludlow and Ledbury. 

 I have for your examination an interesting specimen of this fish from the upper 

 limits of the grey beds which pass into red sandstones higher in stratigraphical 

 position than the true Auchenaspis grits, thus furnishing a very unequivocal proof 

 of a fossil fish passing the physical limits of its assigned position, and caught, flagrante 

 delicto, going upwards into beds which contain other species of Pleraspis and Ccpha- 

 laspis than those with which the truant Auchenaspis should have associated. 



I have also the pleasure of introducing to your notice a head of Cephalaspis from 

 beds at the base of the grey beds whicli contain the Auchenaspis Salteri, and these 

 beds pass into red sandstones with -Silurian shells, and from them conformably into 

 the Uownton sandstones which rest at the summit of the Silurian System. There are 

 also among the specimens I now exhibit some good examples of the lower Old Red 

 plants. 



ThetracksofthelowerOldRed Sandstone, to which I would call your attention, are 

 developed on a large slab measuring 3 feet 2 inches by 2 feet 4 inches. That well- 

 known geologist, the late Rev. T. T. Lewis of Bristow, the friend and coadjutor of 

 Sir Roderick Murchison, when on a visit to the quarries of Puddlestone near 

 Leominster, saw this slab resting in situ on the upper working beds of the quarry. 

 He had it carefully quarried and conveyed to Bristow. A few days before his death 

 he expressed a wish that I might become the possessor, in memory of many happy 

 days we had passed together among the rocks of the Old Red and the hills and vales 

 of Herefordshire. As an instance of the ripple-marking of waves that have for 

 myriads of ages ceased to flow, this Old Red slab would be a treasure to the geologist ; 

 but another feature presents itself, for we find that some animal has wended its way 

 directly across the ripple-marks, leaving the impressions of its movements aa 

 distinctly marked as the human foot-tracks of the limestone of Guadaloupe. These 

 tracks are 1 £ inch in length ; and not only is the trail preserved, but even the 

 folding of the sandy mud, by the indentation of a fish's defence, or a crustacean's 

 tail is preserved, and the raised surface of the old sea-shore, or littoral deposit, stands 

 out in bold relief. The stereoscope gives a slight idea of the remarkable indentations 

 of this slab. Since I came into this room I have met with a brother geologist, the 

 Rev. Mr. Smith of Peterhead, who recognizes these tracks as appearing in the Old 

 Red Sandstone of Rhyme, Aberdeenshire. 



On the Rocks and Minerals in the Property of the Marquis of Breadalbane. ' 



By C. G. Thost. 



The district described in this paper extends for 100 miles from east to west. The 

 rocks are chiefly mica-slate, but talc-slate, chlorite slate, and hornblende rocks are 

 also very common in large masses, and in the north and north-west gneiss and 

 granite. Calcareous varieties of the mica-slate also occur, sometimes in lenticidar 

 masses of nearly pure limestone with 90 per cent, of carbonate of lime. Clay-slate 

 likewise appears very high up on the north side of Ben Lawers. The strike of the 

 rocks is generally E. and W. ; their dip low and various, especially where affected 

 by the intrusive rocks or the ridges and veins of quartz. The igneous rocks are 

 chiefly porphyries and greenstones, well seen at the Tomnadashan Mines on the 

 south side of Loch Tay. In that place the greenstones are evidently the older rock 

 as broken up by the porphyry, which has also introduced the mineral ores. These 

 are seen in it everywhere, but in the greenstone only where in contact with the 

 porphyry. These ores are, silver ore, copper pyrites, grey copper ore, iron pyrites, 

 and molybdena. They are most abundant near the greenstone, and often surround 

 the fragments as if the fluid mass had cooled sooner in these places, and thus col- 

 lected the metallic matters in more abundance. Near the richer deposits of 

 ore, other minerals, as calc-spar, in scalenohedron macles, dolomite, quartz, and 

 sulphate of barytes, also occur. Mines presenting similar conditions are known 

 at Ardtallauaig, about a mile distant, and in many other places. Indeed the hills 

 east of Loch Tay near Taymouth literally swarm with veins of copper pyrites, iron 

 pyrites, and galena. 



A serpentine vein near the upper end of Loch Tay contains chromite, and near 

 it the mica-slate has the mica replaced by graphite in considerable beds. 



