CHALK. 



perfect butterfly, an infinity of minute and beautiful 

 little creatures have escaped. This circumstance 

 seems not a little to have perplexed the old naturalists. 

 How a creature, which ordinarily produced a beauti- 

 ful butterfly, should, at certain times, produce myriads 

 of other smaller insects, was one of those hidden 

 secrets of the creation which they knew not how to 

 fathom ; and we find even the great Swammerdam 

 mentioning it as " a thing very wonderful, that 545 

 flies of the same species were produced from the 

 chrysalides of four butterflies, so that the life and 

 motion of these four creatures seems to have transmi- 

 grated into those of the 545 others ;" and even the 

 philosophical Ray at first thought that it arose from 

 some defect or weakness in the caterpillar which 

 would prevent the perfect development of the but- 

 terfly ; and therefore, in order that the maxim, 

 " Natura nihil frustra fecit," should not be defeated, 

 she stopped short, and formed them into more im- 

 perfect animals. And in the argument which he sub- 

 sequently used in his admirable work, " The Wisdom 

 of God in the Creation," against the doctrine of 

 equivocal generation, we find the same learned author 

 thus expressing himself: " You will say, How conies 

 this to pass? Must we not here necessarily have 

 recourse to a spontaneous generation? I answer, 

 No. The most that can be inferred from hence is a 

 transmutation of species. One insect may, instead of 

 generating another of its own kind, beget one of a 

 different. But I can by no means grant this. I do 

 believe that these flies do either cast their eggs upon 

 the very bodies of the fore-mentioned caterpillars, or 

 upon the leaves, upon which they feed, all in a string, 

 while those hatching eat their way into the body, 

 where they are nourished till they are come to their 

 full growth. Or it may be, the fly may, with the 

 hollow and sharp tube of her womb, punch and per- 

 forate the very skin of the ercua, and cast her eggs 

 into its body. The discovery of the manner of the 

 generation of these sorts of insects I earnestly recom- 

 mend to all ingenious naturalists as a matter of great 

 moment. For, if this point be but cleared, and it be 

 demonstrated that all creatures are generated unequi- 

 vocally of parents of their own kind, and that there 

 is no such thing as spontaneous generation in the 

 world, one main prop and support of Atheism is 

 taken away, and their strongest hold demolished, 

 they cannot then exemplify their foolish hypothesis 

 of the generation of man and other animals at first, 

 by the like of frogs and insects at this present day." 

 In what a striking point of view do the arguments of 

 this good man appear, now that it is known that the 

 suppositions upon which some of them were founded 

 so completely correspond with what takes place in 

 nature ; the only part of them not being found to 

 be strictly correct being the idea, that these parasites 

 laid their eggs on leaves which might be frequented 

 by the caterpillars, an idea evidently derived from the 

 general and incorrect principles to which the pre- 

 sence of blight is usually attributed, and to which we 

 have alrea.dy alluded in our article upon that subject. 

 These little animals, of which we probably possess 

 1500 British species, are highly beautiful in their 

 form, and their colours vie with those of the humming 

 birds. We find gold and purple, copper and green, 

 intermingled in the most elegant order, thus forming 

 exquisite microscopic objects, whilst many of them are 

 highly singular in their appearance. In fact, they 

 appear to be the counterparts of the cercopides 



amongst the homoptera, possessing, like them, the 

 power of leaping to a very great distance, although 

 their legs are very seldom incrassated. This, how- 

 ever, is the case in the typical genus Chalcis, of which 

 we possess several British species, but which, singularly 

 enough, do not possess saltatorial powers, although 

 their posterior femora are very large. The genera, 

 of which the investigation has been greatly neglected 

 until recently, are very numerous. 



CHALK. This universally diffused substance is 

 too well known to need any particular description of 

 its external characteristics. We have manifest proofs, 

 in our own country, that this deposit must have 

 experienced very considerable changes in its geolo- 

 gical arrangement by the action of water ; for the vast 

 beds of gravel which are still employed in the formation 

 of roads, &c., have evidently been rounded by attrition, 

 after their separation from the chalk by which they 

 were originally surrounded. In England, chalk ex- 

 tends with little interruption from the coast of York- 

 shire to that of Devonshire, while a series of hills 

 extends from Wiltshire to the coast of Kent ; and a 

 branch from the centre of the latter ranges to the 

 Sussex coast near Brighton. The Isle of Wight basin 

 comprehends the district between Newport and that 

 island on the north, Brighton on the east, and Dor- 

 chester on the west. In Europe, the chalk extends 

 through France and Poland into Russia, and thence 

 to the south of Sweden, is said to occur near the 

 mouth of the Elbe, thence to Flamborough Head in 

 Yorkshire, and thus completing a circuit which may 

 be termed the chalk basin of Europe. 



Chalk forms, by its extent and distinctive cha- 

 racters, one of the most remarkable mineral features 

 of England. It would seem as if a considerable inter- 

 val of time had elapsed between the completion of the 

 original chalk beds and the deposit of others upon it ; 

 for the surface of the chalk at its boundary with the 

 superincumbent layers, bears marks of having under- 

 gone, during that period, a partial destruction after it 

 was consolidated. There is spread over it a stratum 

 of debris, consisting chiefly of flints washed out of its 

 mass. Moreover, the surface is irregularly worn into 

 numerous cavities, of which many are deep and filled 

 up with the same debris. At the junction of the 

 chalk with the sand and gravel of the plastic clay 

 formation, deep indentations are observed on its sur- 

 face, which are sections of long furrows and cavities, 

 apparently produced by the action of agitated water 

 before it was protected by the covering of clay. The 

 enormous quantity of chalk flint pebbles, completely 

 | rolled and rounded, which are found in the plastic 

 | clay to the south of London, show that the chalk 

 I itself must have been consolidated before that partial 

 | wasting of its upper strata by water. To this hydraulic 

 action, Cuvier and Brongniart ascribe the irregular 

 1 furrows and ridges on the surface of the French chalk, 

 j and the Mucdon breccia. The immense scale on 

 ; which this destruction was carried forward may be 

 | inferred from the vast extent of the English pebble 

 | beds. That a long period of time probably intervened 

 between the deposition of the chalk and of its clay 

 coating is rendered probable also by the total differ- 

 ! ence of the organic remains found in the two strata.. 

 The band of chalk which stretches across the east- 

 ern and southern counties of England, from Yorkshire 

 to Dorsetshire, is to be regarded merely as the west- 

 ern edge of a most extensive tract of this formation. 

 Stretching from the Thames to the Don, the chalk 



