ings, has reason to regret that this freestone abounds in its vicinity.”

"1

"But surely," said Harry, “it is foolish to use such a perishable stone. If I were an architect, I would build with granite, cut so smooth that not a drop of rain could find a lodgment upon it. Then I need not fear disintegration."

"Notwithstanding the defect I have mentioned in this freestone," resumed Mr. Beaufoy, "its surface, in the neighbourhood of Oxford, near the foot of the high ridge of Shotover, is covered for miles with quarries. In this spot you perceive, from the section, that a stratum of Kimmeridge clay lies over the coral-rag; by the latter term you must understand is meant the whole series of freestone, madrepores and sandstones I have just described.

"In one of the quarries the upper surface of the freestone has been stripped of its covering of clay, and bears marks of having been subjected to the action of water, before the clay was deposited upon it: small cup-shaped cavities appear to have been worn into the substance of the stone, which is also traversed by many perpendicular rents and fissures, into which the clay has insinuated itself.” “

in that spot.

CUP-SHAPED HOLLOWS.

373

"I am glad the quarry happened to be opened Papa, is it not probable that those cup-like hollows were worn by the waters in which the madrepores lived?"

"I should think not," replied Mr. Beaufoy; "the stratum containing madrepores lies beneath the freestone. If these hollows may be compared with excavations of a similar form, which I have mentioned as occurring in granite, I should rather suppose they were formed after the retreat of that ancient sea had left the freestone exposed, like the granite of Cornwall, to the influence of the weather.

"The coral-rag, or fossil-madrepore, lying beneath that freestone, is the highest considerable deposit of those lithophites which has been found in this country; but in the Netherlands, the Maestrecht beds, which lie immediately above the chalk, are rich in fossil madrepores."

"Then here is another proof that the position of the strata with regard to each other is not always the same. Mamma told me a curious fact of this

kind.

She said, that in Scotland there is an instance of beds containing coal resting immediately upon granite-while in England coal has been

1 Conybeare, 189.

found only between the mountain and magnesian limestones." 1

"True, Harry. These are some of the examples which teach us that our knowledge of the structure of the Earth is yet in its infancy; and that it becomes us to be very cautions in forming general conclusions respecting it. Our present business is

the examination of facts."

"Well then, papa, will you now give me some account of these upper oolites?"

66

Willingly.

The lower member of that formation is the Kimmeridge clay, which we have already noticed as making its appearance at the foot of Shotover Hill. This tenacious soil is often covered with oak-woods; and hence, in Wiltshire, it is known by the name of oak-tree clay. Sometimes it contains beds of bituminous shale; this is the case near Kimmeridge, on the coast of Dorsetshire, where it is used as fuel, and called Kimmeridge coal.

"On the cliffs in that neighbourhood, and generally two or three feet beneath the surface, is found what the country people call coal-money. Two stones set edgeways in the earth, are covered with a third, and in the cavity thus formed, there lie See page 241.

pieces of coal of a circular form, from two to between three and four inches in diameter: one side of these pieces is flat and plain, the other convex, and adorned with mouldings. The origin of these singular deposits is, I believe, unknown, but the pieces are supposed to have been either amulets or money. The bones of some animals being usually

1

found with them, 1 seems to favour the idea that the motive of deposition was connected with some superstitious observance, but of what nature, it is impossible to determine."

"I think the motive must have been superstitious," said Harry. "Coal-money of that size would be very cumbersome, as well as dirty and unpleasant besides, a material so easily obtained, would hardly answer the purpose.

"Now, papa, we have only one stratum left to consider. Why should this limestone be called Aylesbury or Portland? Those places are a great way asunder."

66

They are so; and serve to designate the two extremities of this formation, so far as its position has been ascertained in England. This freestone makes its first appearance near the village of Stukely, a few miles north of Aylesbury; and accompanying, through a narrow tract, the course of

1 Conybeare, 177, &c.

raised the tin-stone, convey it from the rock to the beach, on account of the heavy swell and surf. He was therefore obliged to be inactive during the whole winter; but the short interval in which he was able to work, amply repaid his persevering labour, and acquired for his mine the reputation of a successful adventure..

"The workings of this singular mine were confined to the large vein of porphyry, or elvan, which I mentioned; and in the year 1791 the whole depth of the workings was only about twenty-six feet, and eighteen in breadth. At that time eighteen men were employed upon the rock between the tides; they worked for two hours in emptying the mine of water, and six hours afterwards in breaking and raising the tin-stone, with which they filled about thirty sacks every tide. From the insular situation of the rock, the ore must have been conveyed to the beach opposite in boats, and hence it probably received its appellation of the WherryMine.

"In the following year the undertaking became more productive; nearly three thousand pounds worth of tin were raised in the course of the summer, and great improvements were made in the machinery. A steam-engine was erected on the