. Edinburgh journal of natural history and of the physical sciences. AND OF THE PHYSICAL SCIENCES. 19 MINERALOGY. SINGULAR SECTIONS OF A KENTISH TLINT. The common flint is found in spherical masses enibotlded in the chalk forma- tions, and the manner in which it has there been formed has fj;iven rise to consider- able discussion among g'ologists. It is certainly a singular circumstance to find in extensive strata of chalk, which is a substance almost entirely composed of pure carbonate of lime, isolated mass-^s of Hint, formed of silica, or quartz. I\Iost com- monly the nucleus of these flint
. Edinburgh journal of natural history and of the physical sciences. AND OF THE PHYSICAL SCIENCES. 19 MINERALOGY. SINGULAR SECTIONS OF A KENTISH TLINT. The common flint is found in spherical masses enibotlded in the chalk forma- tions, and the manner in which it has there been formed has fj;iven rise to consider- able discussion among g'ologists. It is certainly a singular circumstance to find in extensive strata of chalk, which is a substance almost entirely composed of pure carbonate of lime, isolated mass-^s of Hint, formed of silica, or quartz. I\Iost com- monly the nucleus of these flint nodules consists of an animal or vegetable substance, as a shell-fish, coral, or piece of flustra, or sponge; but frequently no such mat- ters are found. The nodu:es, too, assume various shapes, and seem to be moulded according to the cavities of the chalk in which they are surrounded. From the ap- pearances of these nodules, it is evident that they have been in a fluid state, previous to their assuming suc-li shapes, either from the agency of intense heat or of a liquid menstruum, or perhaps from the combination of both these means. The accurate experiments of modern chemists have shown us tiiat silica may be liquified with the greatest ease in combination with either of the mineral alkalies. Thus, if silica and soda be subjected to the intense heat of a furnace, it liquifies into a glass; and if this glass be taken and agnin subjected to the agency of water, heated under a highly-condensed pressure, the silica will be dissolved, and will be deposited, on cooling, around the ci^ge of the vessel. Wlicn combined with a large proportion of the alkali, and under very minute mechanical division, silica may also be dissolved in water at the ordinary temperature of the atmosphere, thus forming the substance called liquor of The fracture of flint nodules usually pre- gents a dark opaque ground, clouded with whitish and dork gray spots and patches. Some of these often assume very
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