Imagini ale paginilor
PDF
ePub

approximately deduced. During 1837, there fell 22.81 inches of rain; and the prevailing winds were S.W., S., N.E., and W.—the least prevalent being the S.E. This is the general summary through the year :

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small]

This
may

be deemed a tolerable view of the Climature of Hartwell for the present; but, as before remarked, the improved system of observation and registry now in practice there, will inevitably produce results of a more advanced and accurate character. And the object is well worth pursuit : for, though some branches of meteorology may long remain among the physical desiderata, yet much may be achieved respecting clouds, vapours, winds, thunder, lightning, hail, rain, ignes fatui, and other perceptible phenomena of the lower regions of the atmosphere. Considerable advance has already been made in inquiries as to the light, heat, specific gravity, moisture, electricity, and constitutional agents of our envelope; but the questions are so beset with difficulties, that our utmost knowledge in this respect does not grasp sufficient facts to reduce the various and uncertain phenomena to formal rule, or to establish anything like a certain theory. The zeal now exerted, however, in various observatories, as evinced by many published and widely-circulated registers, will very shortly set the long-prevalent fancy for the lunar cycle at rest, by which the revolution of the moon's nodes is to place everything exactly as it was nineteen years before.

6. GEOLOGICAL NOTICES.

The extensive Vale of Aylesbury has evidently been denuded and scooped out by the action of water; the lithological peculiarities are therefore seen in a very detached and irregular manner. But the whole pertains to the upper part of the Jurassic system, known as the Purbeck formation.

Although Smith's celebrated map gave the substantial view of Buckinghamshire, it required much circumstantial correction; and this it received at the hands of my friend Dr. Fitton, when he was pursuing his elaborate inquiries into the strata below the chalk. This eminent geologist remarks, that one of the most prominent circumstances in the upper part of the sections hereabout, is the contrast between the arrangement of the sands and fuller's earth, or ochreous clay, and that of the beds which represent the Purbeck formation immediately below. The appearances presented, clearly shew that an interval must have elapsed between the deposition of the Purbeck strata and that of the lower green-sand, during which the surface of the former was disturbed, by the operation, no doubt, of water. He gives the following series of successive beds on a section disposed in the descending order of the strata, commencing with the lower green-sand, in a

[ocr errors]

PIT AT BISHOPSTONE, IN “CHURCH FURLONG," BELONGING TO DR. LEE.

ft. in.

1 0

1. Soil bearing corn.
2. Fuller's earth; greenish and brown. Thickness very irregular

1 in. to
In this bed are iridescent mytili, like those of the bed 7, below, and of

the sections at Whitchurch. 3. Rubble; white, freshwater limestone, decomposed: containing cypris and casts of

small paludinæ, in calcareous spar

:

4 0

[ocr errors]

ft. in.

[ocr errors]

2

.

4. Clay and stone :-
a. Light olive greenish fuller's earth

( 4
b. Soft limestone

0 6 c. Fuller's earth, like a.

0 2 d. Stone, like b.

0 3 e. Fuller's earth

1 5 5. “Sandstone,” so called; firm, grey, and whitish, granular calciferous grit. It has distinct

traces of the lines of deposition, and on the surface some approach to ripple-marks.
Quære. Does it represent the grit of the Hastings sands?

6 in. to 0 9 6. Sand, alternating with ochre and clay:a. Sandy ochreous clay

0 2
b. Dark greenish fuller's earth .

0 2
c. Greenish grey sand, mixed with calcareous matter, and including
scales of fishes.

0 7

0 11 7. Fissile, calcareous clay, or marl, passing into stone

16
In the upper part are iridescent mytili, like those of 2, above, and of the pits
near Whitchurch.
a. Dark, bluish grey, very fissile clay, containing cypris in great numbers, an

oblong unio, and small scales of fishes. (Lepidotus.)
b. Clay, somewhat harder, less plastic.
c. Clay, lighter coloured, and still harder; approaching to stone.

All these divisions coñtain cypris valdensis, and another species; a small smooth

modiola, a striated species; and cyclas parva.
8. “Pendle” (Purbeck): fissile, argillaceous limestone; here of a dark grey colour; in

another adjacent pit almost white: containing cypris ; casts of cyclas parva, some of
which include casts of cypris ; striated modiolæ ; small paludinæ; and other small
univalves, as in the Malm of Garsington

4 in. to 0 6 In some of the pits hereabouts, the “ Pendle” contains also a depressed planorbis,

as at Workley, in the Vale of Wardour; with potamides carinatus.
9. “Bottom Rock” (Portland). This, in one of these pits, is an agglomerate of fragments

of shells; of a dark bluish hue, specked with white. In an adjacent pit, it abounds
with trigonic and other Portland fossils. Thickness not ascertained. The beds

below are not visible, and are unknown to the workmen.

The upper part of several other pits near Bishopstone (as at Southwarp and the vicinity of Dinton) agrees with the foregoing list, in exhibiting an alternation of clays, more or less like fuller's earth, with ochre and ferruginous sand: and the very dark clay which includes iridescent mytili occurs in so many places that there can be little doubt of its former continuity throughout this part of the country. It is particularly distinct on the side of the road from Whitchurch to Winslow, near the turn towards Dunton, about eight miles from Bishopstone; where, besides the usual mytilus, it contains a natica and another spiral univalve (melanopsis ?). Beneath these clays and sands is, universally, thin slaty marl or limestone, with alternate thin beds of clay, containing everywhere the same fossils-cypris, modiola, and spiral univalves--among which are paludina, a planorbis, and perhaps some other species. The whole group, therefore, clearly represents the strata above the Portland stone at Garsington, and in the Vale of Wardour; and is, no doubt, the equivalent of the “ Slate,” the “Cap," the “Dirt,” and the other lower beds of the Purbeck formation, on the Dorsetshire coast.

This is extracted from the fourth volume of the second series of the Transactions of the Geological Society; where is also a table of the beds of a sand-pit at Stone. As this, however, only extends to a depth of fifteen feet, and is not opened in the place most favourable to the display of the superior strata, it is better to proceed to such observations as we have been able to make since Dr. Fitton's exploration. But the having met that gentleman at Aylesbury in the progress of his labours, is among the pleasing recollections which I must ever retain of that neighbourhood.

The environs of Hartwell consisting, as before stated, of the rocks of the upper oolitic group, even the surface exhibits the outcrop of a series of beds. Thus, to begin with the neighbouring village of Stone, in digging wells about the apex of the hill, they have hard work to obtain water at a less depth than fifty feet, and occasionally it is requisite to penetrate twenty feet lower. One section gave successive thin layers of vegetable mould, yellow loam, white sand, white rock, dark clay, rubble stone, and then ten feet of blackish clay, and finally thirty feet, or upwards, of hard bluish limestone. But about half way down the hill, towards Bishopstone, fifteen feet of rubbly limestone succeeded immediately to the vegetable mould, then eight of loam, and finally three of the bluish stone, when the springs were reached. Near the Bugle Inn, close to the park wall, however, the rubbly limestone was absent, and they had to descend several feet into the Kimmeridge clay, before they could obtain water, instead of getting it immediately below the compact limestone. This latter stratum is not above two or three feet thick hereabout, even disappearing altogether a few hundred yards nearer to Aylesbury, which has induced the erection of a brick-kiln there, where excellent red bricks are produced with ease.

Another variation in the stratification is observed in a field behind the

Bugle Inn, beyond the Rood Gardens, where, immediately below the vegetable mould, a depth of several feet consists of very undulating striæ of brown sand, and of yellow, in separate patches, both formed of triturated rolled quartz, as clean as if it had been washed. There is, however, this difference, that, whilst the yellow has few particles smaller than two hundredths of an inch in diameter, the generality of the brown are not above half the size: both have a few small pebbles from the bigness of a pea to that of a nut, and an abundance of black ferruginous incrustations, frequently containing a heterogeneous kernel. On the road to Stone, there occurs a stratum of fine, brilliantly white sand, which, from its cropping out near the surface, has been dug with great facility over the space of about an acre. The purest is obtained from the depth of a dozen feet, and proves excellent in the manufacture of glass, as evinced in the prisms and spheres that Dr. Lee has had made of it, for experiments.

The fossils having been carefully collected, through the praiseworthy encouragement held out to the various labourers, the geologist finds a most interesting feast laid out for him in the Hartwell Museum ; besides duplicates being abundantly furnished, by the kindness of Dr. Lee, to all amateurs, The elaborate collections of Z. D. Hunt, Esq. of Aylesbury, also teem with these “medals of Creation,” and greatly assist in illustrating this locality. The characteristics of the limestone here, are casts of ammonites and trigonias, which meet the eye in every hole, corner, and rough wall; whilst the oysters, mostly the ostrea expansa, stand third as to number, and from being of a stronger texture, have preserved their shells. The ammonites, however, are in such profuse abundance around Hartwell, that a word or two may

be tolerated upon so distinguishing a feature of the basin ; especially as those in the Kimmeridge clay have their pearly or nacreous coat as perfect and iridescent as when fresh from their native seas.

Although, without going far above or below the oolitic group of strata,

*

* The sign or cognizance of the Bugle Inn, near the Park, is a huge ammonite let into the house-wall.

« ÎnapoiContinuați »