Geological time, like all other kinds of time, can only be measured by the succession of events. If the events considered are constant in their recurrence and uniform in their nature, their number will afford the means of measuring the length of time. Thus the oscillations of a given pendulum, the rotation of the earth on its axis, and its revolution round the sun are sufficiently constant and uniform to afford a basis for our seconds, days, and years. Of such uniform and constantly recurring events geology affords no examples by which we could measure the length of geological time.

The Original geological survey of South Wales was made under the direction of Sir Henry de la Beche. The exact date of its commencement is uncertain, but I am informed by Mr. Aveline that in 1840, when he joined, the staff was engaged in the neighbourhood of Cardiff, and in 1841 Bamsay on his appointment found that the survey had progressed westwards into Pembrokeshire, and was at work at Tenby and St. David's. By the end of 1815 the maps had all been published. A complete list of the names which appear on them consists of H. T. de la Beche, J. Phillips, D. H. Williams, A. C Bamsay, W. T. Aveline, J. Bees, T. E. James, W. E. Logan, H. W. Bristow, and H. B. Woodward.

We now come to the second o rder of the Trilobita, which Beecher (loc. cit.) calls the Opisthoparia. In common with the third order, the Proparia, compound paired eyes are usually present, and these are invariably situated on the free cheeks, which form part of the dorsal surface of the head-shield.

All students of Carboniferous geology will hail with pleasure Mr. W. Gunn's masterly paper in the August number of the GEOLOGICAL MAGAZINE (p. 342), and it is only to be regretted that the publication of such important stratigraphical facts should have been delayed for so long; but however useful from the numerous facts it contains, I must take exception to the deductions made from them. The paper is a remarkable one, because, while having for its object the correlation of rocks which occur over a wide expanse of country, no appeal has been made to palseontological evidence to clinch the author's views which are based on purely stratigraphical considerations.

The object of this paper is an attempt to furnish proof of what JL has been a growing conviction in the mind of the writer, that the true age of the Dartmoor granite, and probably its associated line of bosses running south-westwards into Cornwall, might be referable to an interval or period of geological time between the Lower and the Upper Culm, or Carboniferous system.