know of no fact inconsistent with the view, which Professor Wyville Thomson has advocated, that the modern chalk is not only the lineal descendant, so to speak, of the ancient chalk, but that it remains in possession of the ancestral estate; and that from the cretaceous period (if not earlier) to the present day the deep sea has covered a large part of what is now the area of the Atlantic."

Accepting, therefore, this doctrine of the continuity of the chalk, and, consequently, its intimate relationship with our subject, let us endeavour to make some slight acquaintance with the microscopical characters of the common Kentish chalk. In order to do so, some little preparation is necessary. Take a small quantity of chalk in powder, say, two ounces, and place it in a glass bottle holding about a quart. Water is poured in upon the chalk until the bottle is nearly full. The whole is then shaken up, when it resembles milk in colour and consistency, and placed in some position where it remains undisturbed for half an hour. The heavier particles will have sunk to the bottom, the lighter remain suspended in the water, which latter is drawn off, and fresh clear water added, then the bottle may be stood aside to settle as before. This process is repeated again and again until the water is no longer turbid, after standing for a few minutes. The sediment, or deposit, at the bottom of the bottle will be found to be very much

less in bulk than the original quantity of chalk experimented upon, but it will contain just what is required for microscopical examination. If we take a little of this sediment, and place it on a slip of glass, then submit it to the microscope, we shall find it to be composed almost entirely of delicate little shells, those called Globigerina predominating. These shells are carbonate of lime, easily dissolved by acids, the empty, untenanted houses of Foraminifera. That which has been washed away in the washing process consisted partly of the broken fragments of similar shells, and partly of amorphous granules. Hence, therefore, the microscope teaches that chalk consists, for the most part, of very minute shells and fragments of shells, which were inhabited by animals that lived and floated in the ocean thousands of years ago. By their identity of size and form, it is not difficult to recognise in them the shells of Foraminifera, belonging to precisely the same species, in some cases, as those which are found living at the bottom of the sea in the present day.

D'Orbigny computed that there were near four millions of such little shells in one ounce of sand from the Antilles. According to this computation a cube of chalk of six inches in diameter in each direction, and weighing sixteen pounds, would contain the entire shells of not less than 1,024 millions of little animals, and the broken fragments of nearly as many more. Such immense numbers are outside the range of our experience, and we can form no conception of them. Suffice it to say that one ounce

would contain the shells of more animals than there are human beings in the great metropolis of London. But what an infinitesimal fraction this ounce would be of the number of shells of these animals, living

or dead, found scattered over the globe. Deep-sea soundings bring them up from the greatest depths that the line has yet reached, whole catacombs of them are entombed in the chalk and limestone rocks; they are scattered amongst the sand of the sea shore. In Europe and Asia together they cover thousands of miles. They may be found almost everywhere. The traveller who thinks he is out of their reach on the plains of Egypt is mistaken, for if he attempts to climb the pyramids of Ghizeh, he must do so by trampling on myriads of Foraminifera, imbedded in the nummulitic limestone at its base, which, could they but speak, might tell him of days, long before the toiling Israelites were making bricks without straw, of days long before Solomon was King of Jerusalem, or Elijah girded himself to run before Ahab to Jezreel (fig. 11).

In order to test the accuracy of other observers, as well as to procure some new determinations of the number of organisms approximately to be found in chalk, we undertook the experiments some years ago, of which the following is a summary :-An ounce of chalk, as taken from the pit, was subjected to the washing process already detailed, the lighter fragments being washed away, until a sediment was left of nearly pure foraminiferous shells. Half of this was cleaned, as much as possible, by boiling in caustic potash, and ultimately it was demonstrated that this supplied sufficient material to mount one hundred and ninety microscopical slides, of equal character, indeed the whole of that number were prepared, and compared. Each of these slides was estimated to contain one thousand shells, based upon the actual counting of two or three. So that, by calculation, it could be shown that in one ounce of chalk there were 400,000 shells.

Afterwards, and for greater security, another ounce of chalk was washed, even more carefully, and the calculation then showed upwards of half a million of entire shells, without reckoning the fragments which had been washed away, or probably the thousands that had been decanted off with the water in forty or fifty washings. Hence, it is evident that the maximum is not reached when it is affirmed that, at least, half a million of the shells of Foraminifera were contained in each ounce of chalk from that pit. The lump of chalk procured as the basis of these experiments weighed sixteen pounds, or 256 ounces, and consequently contained the shells of 128 millions of Foraminifera. Such a number is easy to name, but not so easy to imagine, a number which would occupy a person ten years to count, even if he could continue to count sixty per minute, for twelve hours daily.

Professor Ehrenberg, the celebrated German microscopist, calculated that there are one million and