Midland Naturalist/Volume 01/A Piece of Chalk
A Piece of Chalk.
By Fred. F. Grensted, Maidstone.
Only a piece of chalk, of no appreciable value, and yet it has preserved a decipherable record of marvellous events which happened numberless ages ago! Judging by analogy, where England now stands, water a mile or two in depth was "once upon a time" lashed into ocean waves by the passing wind. Travelling in thought to the bottom of this unnamed sea of an unknown era we find the ocean floor covered with a white, soft, sticky mud, the exact counterpart of that which is found in the Atlantic at the present day. This mud would be almost entirely composed of very minute but lovely shells, which are now known by the generic name Foraminifera. They are so small as to require the aid of a good microscope to reveal their lovely forms. As in thought we gaze upon the scene with eyes enlightened by modern scientific research, we see these shells slowly falling through the water like a snowstorm, unceasingly day by day and your by year, as their tenants, once alive and swimming about in the water above, die off in countless myriads. Thus, generation after generation died and sank to the ocean bottom, and in turn was buried beneath the remains of its offspring. Thus, slowly but surely, fragment by fragment, were the chalk cliffs and downs of Albion deposited beneath the deep waters of a mighty sea.
All who may desire to be satisfied that this is no legend or fancy picture, have within easy reach the means of forming en independent judgment, They have merely to take a piece of chalk, or preferably some of the naturally formed powder found in chalk pits and on exposed cliffs, and ascertain of what it is composed. I will describe an easy and effectual method of doing this. If the natural powder is not within reach, any soft piece of chalk reduced to powder by being scraped with a knife will do almost equally well. Place some of the powder in an ordinary medicine bottle, fill up with clean water, and shake vigorously for some time. Then let the milky fluid settle for about ten minutes. Next, by means of a syphon, easily made with a piece of indiarubber tubing, draw off the contents of the bottle to within half an inch of the bottom. Fill up the bottle with fresh water, shake up as before, once more let the fluid settle, then draw off with the syphon to within the same distance of the bottom. Do this again and again until the fluid ceases to be milky, and becomes, as it were, diffused with fine dust, the separate grains of which will be plainly visible when the bottle is held close to the eye against a bright light. These grains are the treasures we are in search of. Besides them, however, the bottle will contain some small particles of chalk. To separate the one from the other is our next object, and it may be effected by shaking the bottle well, and instantaneously drawing off the fluid into another bottle by means of the syphon. This operation, if properly done, will remove the lighter shells and leave some of the heavier and the chalk behind. Having allowed the shells in the second bottle to subside, the water must be drawn off by the syphon. A good layer of these tiny shells may be obtained by repeating the process above described over and over again. The bulk of the water having been syphoned off, the shells should next be carefully filtered on blotting paper, then dried and stored in a pill box, or other convenient receptacle.
The shells thus obtained, if the operation has been properly done, should be perfectly clean, though fragments of shells will, of course, be found mixed with perfect ones. In the various stages of the process it is advisable to ascertain by means of the microscope that all is going on well. The method will be found very simple, and I can vouch for its success, for it has yielded me most satisfactory results.
To mount the specimens for the microscope all that remains to be done is to take as many as will lie on the point of a knife and boil them for a short time in a test tube containing a little turpentine. This is done to expel the air from the shells. Transfer a few of the specimens to the centre of a glass slip. add a spot of Canada balsam, and immediately place a thin cover glass on, and when dry finish off according to taste. The slides thus inexpensively provided will then be ready to answer the enquiry "What does the chalk contain?"
This work was published before January 1, 1929, and is in the public domain worldwide because the author died at least 100 years ago.
Public domainPublic domainfalsefalse