town, eaten a deeper and deeper bed vertically down by its own mighty powers? If it has not accomplished such a purpose, what is to be said of the solvent powers of our English rivers, that have, without any display or any thunder, chiselled out such enormous gorges and ravines, many hundred feet deep, through solid masses of the very hardest quartzose rock, as is the case in the border district of England and Wales with those diminutive rivers the Teme, the Onny, and the Wye, where they break through the escarpments presented to them? Those rivers I quote purposely, because it can be shown that where they so break through, there are great dislocations of the strata from causes which are not at all doubtful, but clearly volcanic in their origin, and the channels of the rivers themselves occupy cracks transverse to the direction of the rocks they traverse. And if we compare the two examples-making allowance, of course, for the great difference in every item between the condition of the old red sandstone and plastic clay districts, we shall see that on a small scale, the same phenomena were acted over again in the tertiary epoch which did such great things at the period when the older secondary and transition rocks were ruptured.

That these cracks at Studland are regular fissures, and not accidental channels for rain water, is shown by following them to their source, and measuring their direction. That for instance which is marked 6 in fig. 56, opens upon the shore in continuation of the passage through the lofty plastic clay hills behind, and the opening through the chalk at Threeforked Down, by which the road is traversed from Swanage to Studland, and its direction ranges from S.W. by W. and N.E. by E. Just under the signal-house, where the cliff is from 16 to 20 feet high, the hard beds of sand stone are split vertically down, leaving a space of about three feet between

Fault in the Ravine to the right of the signal-house, Studland.

the walls; on the south side the beds dipping to the N.E. at about 24°, exactly agreeing with the dip at the Red Rock,

of which they are a prolongation. The right side of this crack forms the left of an insulated mass, filling up the middle of the ravine, on the right of which the beds are horizon

tal (fig. 63).

The farther end of the ravine closes abruptly, but the view beyond it is given in fig. 64.

P.C

P.C

P.C

64

C, Chalk. P C, Plastic clay. The arrow shows the direction of the ravine. arrow points out the opening in the chalk at Three-forked Down.

The dotted

Continuing the examination of the surface along this tableland, we discover that a declination of the level takes place from the head of this ravine to the head of that on the south side of the Red Rock, which passes under a cliff of yellow and red sand, extending from under the church-yard, and capped by a bed of whitish sandy clay (used for walls of buildings), which is naturally split into quadrilateral fragments; the dip of these beds being from the southern chalk of Ballard Down. So that Studland may be considered as a square mass of country, leaning upon the chalk on the southern and eastern sides, and dipping from it in those directions, as it would naturally do upon the supposition of its having been deposited upon the slopes of the chalk, and afterwards subjected to the forces of elevation by which the chalk has been deranged.

That this must be the exact state of the case is confirmed by the condition of the country intervening between Studland and the chalk ridge of Ballard Down. The plastic clay behind Studland ranges, in Studland Heath, to a level nearly as high as the summit of Ballard Down itself, but it has been subjected to violent denudating agents, and a deep valley,

rising in the centre, but trough-like on each side, marks the space between the two formations.

The appearance of this district from the coast is shown in fig. 65, and the transverse section across the diluvial hollow is given in fig. 66. It is premature to allude to the connec

Valley between the Chalk and Plastic Clay,-between Studland and Ballard Down.

1, Chalk. 2, Plastic clay.

tion between the diluvial and the uplifting forces, but it may be here safely mentioned, that the very aspect of the district about Studland, from the summit of Ballard Down, and from various stations in the ascent thither, demonstrably convince the observer, that though violent denuding forces have excavated the deep valleys and hollows between the chalk and the sea, these valleys and hollows, whether longitudinal or transverse, owe their primary development to preceding causes, that uplifted, split, and convulsed the lower beds of chalk, and the superimposed tertiary deposits that now only exist in part.

And since we have seen in this investigation, that the lines of direction in these dislocations coincide with the longitudinal and transverse directions of the chalk elevation-and these again with those of the sub-cretaceous formations, it follows, that the derangements in the plastic clay of Studland owe their existence to the very same phenomena as have, in the same linear directions, produced such striking alterations in the arrangement of the country beyond the area of the chalk-field.

Subsequent investigations will more fully explain the extent of these derangements, but sufficient has now been said to illustrate the phenomena of the plastic clay, at its junction with the chalk at Studland Bay;-all of which are, evi

dently, the result of elevating forces, that in this district have left proofs too palpable to be denied.

Presteigne, Radnorshire.

ART. III.-On Hymenotes, a Genus of exotic Orthopterous Insects. By J. O. WESTWOOD, Esq., F.L.S. &c.

THE philosophical principle that Nature, ever ready in resources, arrives at the same result in various methods, is nowhere so capable of demonstration as in the insect tribes, where, owing to their immense numbers, far exceeding in fact the number of all the rest of the species of the animal kingdom taken together, it must necessarily happen, from the necessarily great modification of form exhibited amongst so many animals, that the great functions of existence must be carried on in different ways.

The preservation of the creature, one of the great primary objects of all its energies, as well as of its organic structure (necessary for the display of such energies), is not only effected by active operations, but also by those passive means of resistance afforded by the peculiar structure and shape either of the body or of its different parts. It would carry me into too wide a field to give examples in support of this principle, which must be strongly perceived by all who take more than a superficial view of the workings and works of the creation. The particular group of insects which is the subject of this paper, exhibits an interesting instance of it which it will be worth while to notice, proving as it does that where one organ, having a particular function necessary for existence, is either atrophied or diminished in extent, another organ takes up such function, and thus supplies its place, while at the same time it retains its normal, or as we may say original function. Ordinarily speaking the back of insects is not generally of a solid texture; where solidity is given to it the wings are more particularly membranous; where it is less solid the wings, or more strictly speaking, one pair, become thickened, so as to defend the real wings, which from their large size require to be packed up, (of which the common earwig forms a beautiful example), as well as the back of the abdomen. Such is especially the case in beetles, where the wing-covers attain their strongest consistence, and serve unitedly to form a powerful shield or case, whence the very name of the order, Coleoptera, or wings in a case. In other instanVOL. III.-No. 34. N. s.

3 G

ces we find this shield consisting of a single piece, being then named the scutellum, and which in some tribes of Hemiptera becomes so large as entirely to cover the back of the abdomen, wings, and wing-covers. Such is the case in a singular degree in the genus Coptosoma, the peculiar structure of which I have described in this Magazine (vol. ii. n. s. p. 26). Such is also the case in other portions of the family of Cimicide thence named Scutelleride, and in some singular Hymenopterous insects forming the genus Thoracantha, in one of which (Thor. Latreillei, Guérin) this scutellum exhibits all the appearance of two elytra soldered together. In other tribes, again, we find this shield composed of a piece still nearer to the head, namely the dorsum of the prothorax, which is immensely developed backwards, covering not only the back of the abdomen, but also the whole of the mesothorax and its scutellum, metathorax, and wings. This structure is of much rarer occurrence than either of the former, occurring in various species of Linnæan Cicada, where the armature of this part is most anomalous, and in a few genera of Orthopterous insects, including that which is the subject of this paper: this peculiarity, in conjunction with the saltatorial powers of the insects, their musical talents and herbivorous habits, evidently prove that the order Homoptera of Latreille (to which the Cicada belong) is the true analogue of the order Orthoptera to which these insects are to be referred.

Linnæus, in the earlier editions of the 'Systema Naturæ,' proposed a division in the genus Cicada which he named Foliacea, with the character "thorace compresso-membranaceo;" the insects belonging to this division are truly Homopterous, and now constitute the genus Membracis of Fabricius. The dorsum of the prothorax is of immense size, compressed, not thicker than writing paper, and elevated over the entire body, extending in fact considerably in front of the head.

Felton described two remarkable insects in the Philosophical Transactions for 1764 (vol. liv. p. 55, published in 1765), in a paper entitled "An Account of a singular species of Wasp and Locust," which he had met with in Jamaica. The following is his description of the "locust."

"RHOMBEA Cicada, thorace compresso, membranaceo, foliaceo, subrhombeo, posticè latiore.

The thorax is like a leaf that is raised perpendicularly from the body, and is three times as broad as the body, but the same length. This leaf is very near of a rhomboid figure, a little broader or rather higher over the back, it is membranaceous, probably brownish; (when alive half pellucid, with two spots that are more pellucid or transparent; the larger one is very near the middle, but the smaller lower). The margins are waved, especial