cannot be done equally well in almost any other town of its size in Scotland,--pursue my geological inquiries under cover. On this, as on other occasions, I was struck by the complex and very various forms assumed by the ganoid scales of the Wealden. Throughout the Oolitic system generally, including the Lias, there obtains a singular complexity of type in these little glittering tiles of enamelled bone, which contrasts strongly with the greatly more simple style which obtained among the ganoids of the Palaeozoic period. In many of these last, as in the Coelacanth family, including the genera Holoptychius, Asterolepis, and Glyptolepis, in all their many species, with at least one genus of Dipterians, the genus Dipterus, the external outline and arrangement of scale was as simple as in any of the Cycloid family of the present time. Like slates on a roof, each single scale covered two, and was covered by two in turn; and the only point of difference which existed in relation to the _laying down_ of these massy _slates_ of _bone_, and the laying down of the very thin ones of _horn_ which cover fish such as the carp or salmon, was, that in the massier _slates_, the sides, or _cover_,--nicely bevelled, in order to preserve an equability of thickness throughout,--were so adjusted, that two scales at their edges, where they lay the one over the other, were not thicker than one scale at its centre. Even in the other ganoids, their contemporaries, such as the Osteolepis and Diplopterus, where the scales were ranged more in the tile fashion, side by side, there was, with much ingenious carpentry in the fitting, a general simplicity of form. It would almost appear, however, that ere the ganoid order reached the times of the Weald, the simple forms had been exhausted, and that nature, abhorring repetition, and ever stamping upon the scales some specific characteristic of the creature that bore them, was obliged to have recourse to forms of a more complex and involved outline. These latter-day scales send out nail-like spikes laterally and atop, to lay hold upon their neighbors, and exhibit in their undersides grooves that accommodated the nails sent out, in turn, by their neighbors, to lay hold upon _them_. Their forms, too, are indescribably various and fantastic. It seems curious enough, that immediately after this extremely _artificial_ state of things, if I may so speak, the two prevailing orders of the fish of the present day, the Cycloids and Ctenoids, should have been ushered upon the scene, and more than the original simplicity of scale restored. There took place a sudden reaction, from the fantastic and the complex to the simple and the plain.