For some time past we have been drawing attention to some of the dicta of Geology, which appear to have a less solid foundation than they should have to authorize the positive manner in which they have been enunciated. Similar doubts on some points would appear not to be absent from other minds. Mr. Page has just issued a little work reviewing the state of the popular doctrines of our science, and Mr. Sterry Hunt has appropriated to the explanation of the higher Palaeozoic climate Dr. Tyndall's memorable researches on the relations of gases and vapours to radiant heat. Heat, from whatever source it may proceed, passes through hydrogen, oxygen, and nitrogen gases and dry air, with nearly the same facility as through a vacuum, and these gases are thus to radiant heat what rock-salt is amongst solids. Glass and some other substances which are readily permeable to light and to solar heat, offer, as is well known, great obstacles to the passage of radiant heat from non-luminous bodies, and many vapours and gases have a similar effect in intercepting the heat from such sources. Thus, for a vacuum the absorption of heat from a body at 212° Fahr. is represented by 0, that by dry air as 1, while the absorption by an atmosphere of carbonic acid gas is 90; by one of marsh-gas, 403; by olefiant gas, 970; and by ammonia, 1195.

Early in September of the present year, I accompanied my friend Mr. C. Evans in a short excursion to Farringdon, with a view to examining the well-known “Sponge-gravel” pits of Little Coxwell; our intentions being, besides collecting fossils, to trace, if possible, some positive connection, or otherwise, between these reputed Upper Cretaceous Sponge-gravels and the acknowledged Lower Greensand deposits of Furze Hill and Badbury Hill.

Taking up our quarters at Farringdon, we first visited the Sponge-gravel pit near the Windmill public-house at Little Coxwell, where we found a splendid section of the gravel exposed (see section 4), and in a few hours had collected a good supply of fossils;—dip of beds E. by N. 10°, resting, in part at least, upon Kimmeridge clay. Next day we went to Furze Hill, and found near the top of the hill the ironstone concretions described by Mr. Godwin-Austen (Quar. Journ. Geol. Soc, vol. vi. p. 456), containing numerous fossils, all of them, I believe, of Lower Greensand age. These concretions, for the most part, lie scattered about on or near the surface. In one place, however, we found a small section exposed, where the concretions occurred in position, imbedded in light-coloured sand. About fifteen feet lower down the hill, we found the same light-coloured sand, alternating with clay in thin layers, without concretions, and apparently unfossiliferous.

Rozier says, in his ‘Journal de Physique,’ 1782, page 174, that “mention is made in the Catalogue of Davila of a tibia and of a beak imprinted on two different stones.” If there be any other notice in Davila than the passages we have quoted, it has escaped our search.

In 1782, M. Robert de Paul de Lamanon gave, in the Abbé Rozier's ‘Journal de Physique’ (vol. xx. p. 174), an excellent summary of what was then known of Ornithic fossils. After noticing the accounts in Albertus Magnus and other old authors, he goes onto say in his ‘Description de Divers Fossiles trouvés dans les carrières de Montmartre, près Paris, et vues générales sur la formation des Pierres gypseuses,' “M. Rouelle, according to M. Darcet, found in the plaster quarries of Montmartre parts of a bird separated one from the other. I(Lamanon) have seen also in the Cabinet of Natural History of Bordeaux, some bones that it has been attempted to refer to birds; they were found by the Abbé Desbiey in the quarries of Léognan, which are at two leagues from this capital. We can only assert, however, that these isolated bones may have belonged to birds, on the ground that their medullary cavity is very large relatively to their thickness.

Australia offers both advantages and the reverse as a field wherein geology may be studied. Mesozoic strata being absent, or very sparingly developed, the variety of fossils is not extensive; but some of the phenomena observable are by no means devoid of interest.

The very limited portion of the Australian continent which I purpose describing is delineated upon sheet number 1 of the geological map lately issued by Mr. Selwyn,—a reduced sketch-copy of which is enclosed with the present communication (Pl. VI.).

By this map it will be seen that there are at least three classes of strata to be noticed—Silurian, Tertiary, and Volcanic. The site of the Victorian metropolis, together with the suburban townships, comprises the whole of these in various proportions. Melbourne proper, with the exception of its extreme western portion, which is situate on an older volcanic formation, is built almost wholly upon May Hill sandstones and soft laminated shales. The whole of this stratum has evidently been subjected to immense disturbance, it being a matter of no little difficulty to discover a patch many yards in extent within which the beds even approach to a horizontal position. The general inclination of the stratification more often verges on the perpendicular, whilst numerous contortions, folds, and doublings—theupper edges being cut away by denudation, at the same time that the lower are hidden far below the exposed portion—offer an interesting but withal most difficult problem to the geological student.