From the short notices which are to be found about volcanos in treatises on geology, we might often be led into the belief that they were structures so regular in contour that their form was indicative of their nature. In certain cases this appears to be so remarkably true, that I wish to add a few observations to those which have already been written upon the subject. In other cases, however, the form of a volcano does not appear to have any characteristics which distinguish it from other mountains, as will be seen by glancing through the series of views given by Humboldt of the volcanos of South America. The mountains in Iceland are also very rough. When travelling in that country, where I saw and ascended many volcanos, I do not remember that there was anything about their shape more than their steepness and general ruggedness which particularly attracted my attention. The wilderness of form presented to us by such mountains as these is so evidently the combined effect of many and varied causes, that it would be vain to seek a simple explanation for the formation of the whole.

It will probably be conceded, by those who have studied the Somersetshire portion of the British Coal-field, that the correlation of the various parts of it is not, at the present time, so perfect that any attempts to improve it are entirely uncalled for. The following conjectures as to whether some of the facts relied on as proving the commonly-accepted theory of the structure of the Somersetshire Coal-measures, and their general correlation with those in Gloucestershire, may not possibly admit of an interpretation differing from that usually assigned to them; are put forward in the hopes of indicating a line of research which may eventually, when modified by the results of further investigations, lead to a solution of some of the numerous difficulties at present standing in the way of a satisfactory understanding of this extremely complicated district.

Near Kildale, a small village on the North Yorkshire and Cleveland Railway, not far from the source of the river Leven, a railway cutting close to the station shows, in descending order, the following section.

For many purposes it is often desirable to form some approximate estimate of the area occupied by a particular deposit, and in working out the topography of any county or district (especially for agricultural purposes), it is frequently necessary to ascertain the relative extent covered by the various formations. This information, in every instance which has come under my knowledge, has been obtained by measuring on the map with a rule, and entering the results, according to the scale, as so many square miles of surface. Nothing being more uncommon in nature than a straight line of boundary, every one who has made the attempt must be aware how impossible it is to reduce with any degree of accuracy to a geometric figure such lines as those to be found on most geological maps, and having recently had occasion to make a calculation of this nature, for Devonshire, I wish to describe a very simple method which I adopted with success.