Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/66

 peratures and currents, with instruments prepared for the occasion. I must refer to the papers by Dr. Carpenter and his colleagues (to whom I am much indebted for the perusal of the last Report, now going through the press), in the ' Proceedings of the Royal Society'*, for the varied information respecting the composition of sea-water at different depths, the gases contained in it, and the speculations on oceanic currents. The points that more particularly interest us are those bearing on geological investigations.

In first drawing the attention of the Royal Society to the importance of undertaking deep oceanic researches, Prof. Wyville Thomson referred to the recent discovery by Prof. Sars of a small crinoid belonging to an order supposed to be extinct, and which flourished from Jurassic to Cretaceous times ; he suggested the probability of the continuity of the ancient chalk-sea with the present abyssal depths of the Atlantic, as such depths would be but little affected by any of the later oscillations of the earth's crust in the northern hemisphere, as, since the commencement of the Tertiary epoch, they probably had not much exceeded 1000 ft. The result of the first expedition was more than sufficient to confirm the most sanguine anticipations. Dr. Carpenter, on its return, reported that, of the higher types of marine animals which they had discovered, " many carry us back in a remarkable manner to the Cretaceous epoch ;" and, again, it " seems on general grounds highly probable that the deposit of Globigerina-mud has been going on from the Cretaceous epoch to the present time (as there is much reason to suppose that it did elsewhere in anterior geological periods), this mud not being merely a chalk formation, but a continuation of the chalk formation." These views have a high significance and interest. Let us see how far we can adopt them.

The Atlantic abyssal mud has been found to contain from 50 to 60 per cent, of carbonate of lime, 20 to 30 of silica, with small variable proportions of alumina, magnesia, and oxide of iron. Its appearance, when dry, is chalk-like ; but it is to be observed that our white chalk is a much more homogeneous rock, containing from 95 to 99 per cent, of carbonate of lime, while even our grey chalk contains from 80 to 90 per cent†. The larger proportion of cal-

vol. xix. pp. 146-222.
 * Proc. Roy. Soc. vol. xvii. pp. 168-200; vol. xviii. pp. 397-492; and

† Since writing the above, Mr. David Forbes has kindly obliged me with the following observations: — " The specimens of Atlantic mud or soundings which I have examined, differ very essentially from chalk in composition ; and no single one of them (if consolidated) could be entitled to the appellation of