In whatever part of the world we live we can readily discover, by ordinary observation, that there are two great forces constantly occupied in remodelling its surface, from year to year, from century to century.

In that rich storehouse of fossils, the Cornbrash, there occur, as all geologists who have been in the habit of collecting from it are aware, several species of the genus Ostrea, two of which are large and conspicuous shells. One of these is the everywhere abundant and very characteristic plicated form known, as O. Marshii, Sow. (O. flabelliformis, Lamk.?); the other, which is far less common, but by no means rare, is flat and smooth, and sometimes considerably elongated in form. This latter species does not appear to have received a name in this country, but it may not improbably be identical with the O. exarata of Goldfuss (Petrifacta Germaniæ, Theil ii. z. 5, tab. 72, fig. 9), a shell first obtained from the Unteroolith of Gräfinberg.

Those who have taken part in the recent discussions as to the origin of lake-basins are well aware that one of the chief causes which has retarded a settlement of the controversy is the ignorance prevailing as to the true form of such basins. Even as to the Swiss and Lombard lakes, constantly visited as they have been by men of science, the data are extremely scanty and no way reliable. A few soundings made by myself in the Lake of Como, in 1863, and referred to in a paper published in the Philosophical Magazine in the following December, increased my conviction of the importance of instituting careful and exact measurements of the form and dimensions of the beds of lakes, if we were to reason securely as to their origin. I expressed that conviction at the time to an active local naturalist, Don Baldassare Bernasconi, residing at Laglio. In 1865 Signer Gentilli, one of the engineers of the Lombardo-Venetian Railway, being for some months on the Lake, proposed to undertake a regular survey of the bed of the Lake by means of a complete series of soundings, and devised an instrument for measuring the distances traversed horizontally in a boat, corresponding to each cast of the sounding line. Signer Gentilli found two active coadjutors in the persons of the above-named ecclesiastic, and of Dr. Guiseppe Casella, also resident at Laglio, on the Lake.

It has not hitherto been clearly made out in what way these Carboniferous patches are related to each other. Some have considered it doubtful whether the three former are in any way represented in the Coalbrook-dale Field. The prevailing impression is, I believe, that the Clee Hill Fields are quite distinct in point of age from any of the Coal tracts surrounding them, and were formed in a depression sufficiently low to receive the Millstone Grit which we find to be wanting in the extensive Coal-fields to the East and North-east, except, let me observe, along the Western margin of the Coalbrook-dale district, where it is not well developed, but still represented. Eastward of that margin, however, it thins out rapidly, and gives way to the Silurian flooring of that Coal-field.

Geol. Mag. for July, p. 333, in Mr. Marshall Hall's letter on “Terraces in Norway,” for “Moïk Pors,” read “Mörk Foss.”.