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 v.hen 

 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 funtastiu 

 imitations of figures of men and annuals. In 

 the British ]\Iuscum is an agate on which 

 is portrayed a very accurate likeness of the 

 poet Chaucer; and during the French R.e- 

 volution, immediately after the king was 

 heheadeJ, a very rcmarlcablo portrait of this 

 unfortunate monai'ch was discovered dis- 

 tinctly marked in a piece of Labrador spar. 

 So accurate was the likeness, and so curious 

 was this coinci'.bnce reckoned at the time, 

 that a very large sum of money was obtained 

 for it ; and fac-similcs were engraved from 

 it, and worn as rings by the loyal inhabi- 

 tants of Europ'j. In the annexed engrav- 

 ings we have given a fac-simile of three 

 rt^markablc portraits found in a Hint nodule, 

 which may be seen in the Museum of 'Mr 

 Robert Frazer, Jeweller, 17, South St An- 

 drew Street, Edinburgh. 



This mas- of flint, weighing about six- 

 toon ounces, was picked up by mere acci- 

 dent, on the Kent road, near London. On 

 breaking oif a small piece of it, the profile, 

 Xo. 1, was discovered on the surface of 

 the fracture, and immediately recognised as 

 bearing a very striking resemblance' to ths 



flints. By one or other of such processes, then, taking place in nature, we may sup- 

 pose that a quantity of liquified silica has boen dilfused among a bod of chalk. The sm- 

 gular circumstance however is, how it should have collected into the numerous separate 

 nodules in which it is universally found; and this has been attempted to be explained, 

 by supposing that a chemical attraction has taken place between the vegetable or ani- 

 mal remains strewed profusely among the chalk and the silicious matter, by which the 

 latter has been accumulated around, and incorporated into, the minutest parts of the 

 organized substances, thereby forming the petrifactions so generally found in the flint 

 nodules. In those cases where no traces of organization are found, it may he supposed 

 either that the organic structure has been entirely destroyed, or thr.t the silicious matter 

 has been fi'oin the first simply deposited in a cavity or fissure of the chalk. Flint 

 nodules, although composed of the same materials, have not generally the comnact 

 and dense structure of the pebble or agate. Flint is of a more porous nature, and of 

 an opaque and clouded appearance. If a piece of flint be broken, and immediately 

 examined, minute drops of moisture will be seen to ooze out from its pores, afl'ording 

 a proof that water must have originally assisted at its fluidity. It must be remarked, 

 however, that alkaline matter is not found to exist in any great quantity in itt coni- 

 position. From the opaque and porous nature of flints, it has been conjectured that 

 they may have been formed partly from particles in a slate of minute mechanical division, 

 and partly from others in a state of chemical solution. 



general contour of the features of the first 

 warrior and general of the age. The portrait 

 has somewhat the appearance of an enamel 

 p linting ; the figure being of a whitish-gray 

 substance, surrounded by a dark brown 

 ground. As it was conjectvired that, in 

 all probability, the impresc-ion of the figure 

 might penetrate deep into the stone, it w; s 

 slit up neaidy through the centre, when the 

 figures No. 2 and 3 were displayed on each 

 side of the exposed surfaces; and it will 

 not require a very active fancy to discover 

 in these the face and hncamcuts of a mo- 

 narch endeared to the British nation. These 

 two likenesses have actually been recognized 

 and pointed out by different intlividuals, who 

 had no previous knowledge that such a si- 

 milarity had before been discovered ; thus 

 affording a test of the truth of the general 

 resemblance. At the time that these like- 

 nesses were first discovered — about five 

 yeai-s ago — it was looked on as a curious 

 coincidence that the monarch and his prime 

 minister should both be found depicted on 

 one stone by the hand of nature, and by a 

 process which, even with all tlie aids of mo- 

 dern chemistry, we fear we have but imper- 

 fectly conjectured, and endeavoured to ex- 

 plain to our readers. 



F.mt IS not the only substance wliirh is found to contain animal and vogctable 

 n.atter wthin Us nodules. Small portions of moss plants, and other ervpto^amia, 

 «re frequently found, beautifully preserved, in the rock crystal, topaz, and ^ate, w.th 

 .11 the mmute lineaments of their original structure. This affords another proof of the 

 iact that such crystals must have been in a fluid state, without any jreat increase of 

 temperature, at the period when they assumed their soHd form. .Many of these stones 

 " well as jaspers contain various figures assuming the forms of vegetation ; bein" in 

 i-eality, merely accidental admixtmes of various metalUc substances, which, in crj°tal- 



lizing, thus assume the appearance of leaves and stems of plants. Of this kind are 

 the mocha stone, arborescent jasper, landscape marble, &c. Drops of water, how- 

 ever, and portions of air, are occasionally found in such crystals, under circumstances 

 which led Dr Davy to suppose that these have been enveloped in the crystal while 

 under great expansion by heat. On carefully opening the cavities, he found that the 

 water and air diminished in volume, when exposed to tlie ordinary pressure of the 



atmosphere, in some instances to the extent of six to eight times their bulk in the 



chalcedony to the extent of sixty times their volume. 



