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.