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0 TRANSACTIONS OF THE SECTIONS. a group would be made out between the Labrador series, or Upper Laurentian, and the Cambrian. lie considered that the attempt to identify the subdivisions of the pre-Cambrian rocks in distant countries (Britain and America for instance) was pre mature. Calling attention to the two unconformable groups which Dr. Hicks had made out at St. David’s, he felt satisfied that the Cambrian was unconformable to the upper as well as to the lower, and stated that he had himself found fragments of the hornstones, i. e. the Upper pre-Cambrian group, in the conglomerates at the base of the Cambrian. The oldest rocks of N.W. Scotland, of tile Malvern Hills, and of Scandinavia, he thought could at present only be safely called pre-Cambrian. Gth Epoch. Gap between Huronian and Cambrian.—Since we have in Britain certainly two, and in America probably three series of deposits before the Cam brian, and the Cambrian may rest on any one of them, it is impossible to estimate the duration of the period between the Cambrian and the newest of the pre-Cam brian rocks. 7th Epoch. Cambrian.—He referred especially to the labours of Dr. Hicks, and thought that there were no hard and fast lines of demarcation between different subdivisions of the Lower and Middle Cambrian, but only zones of life, and that the boundary-lines between the portions of the series in which these zones of life occurred were continually being shifted. Sometimes, where a change in the sedi ment happened to come between two zones, this was seized upon as marking a con venient place to draw a line. Such a boundary was that offered by the Garth Grit, which comes between the zone of Angelina Sedgwickii and that of JEglina binodosa. No life zone older than this last appears to have been yet made out in the Lake- district. This grit is not a conglomerate formed of fragments of the underlying rock, but is made up almost entirely of (juartz-pebbles, small and well worn, as if derived from a distance. A precisely similar grit occurs associated with some what similar slate low down in the green slates and porphyry in Chapel-le-Dale on the S.E. border of the Lake-district, probably not very far above the horizon of the Garth Grit. It is like the grit which occurs frequently in South Wales in the Caradoc beds, in the Denbigh Grits in North Wales, and in the Lake-district in the Coniston Grits, and in all these cases is known to be far above the base in a conformable series. A great part of the series above this horizon is, in the Lake-district and in North Wales, made up of volcanic ejectamenta. In North Wales the ash and lava seem to have been deposited in the sea and modified by its action ; while in the intervals between the periods of volcanic activity various forms of marine life lived on the muddy bottom, which enable us to correlate the beds with the Bala series. In the Lake-district the sea seems to have been filled up by the immense quantity of material thrown out, and much of the accumulation is supposed to have been sub aerial. In both districts volcanic activity seems to have ceased, while the fauna of the Bala Limestone still inhabited the area ; and subsidence went on while the Bila and Ilirnant Limestones, with a great mass of interbedded and overlying flags, were deposited in North Wales; and in the Lake-district the corresponding deposits, viz. the Coniston Limestone, Fairy-Gill Shales and Ash-Gill Flags (=Lower Coniston Flags), were formed. In South Wales and the western borders of England only a few ash-like beds suggest the not distant line of volcanic outbursts. Scotland, Scandinavia, Bohemia, and America yield a series which, if not in detail, can in a general way be correlated with these. The fact that the Lake-district and North Wales were during this period the seat of old volcanoes, will partly explain the difficulty that was experienced by Prof. Sedgwick and Sir Roderick Murchison in identifying the corresponding beds in the two areas independently examined by them; and the sudden ending of the volcanic deposits may probably account for the local apparent irregularity of the Coniston or Bala Limestone on the underlying series, which induced Professor Sedgwick to make that limestone the base of his upper subdivision, and which has recently been urged as proofs of an unconformity bv Mr. Aveline. Except in connexion with the volcanic deposits, no break has been proved from the conglomerates which form the base of the Harlech group to the top of the Bala series. 8th Epoch. The Gap between the Cambrian and Silurian.—This he thought not strongly marked, and certainly not to be drawn between the Tipper and Lower
