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"The Strata we have been examining are succeeded by a species of stone, often called Bath-stone, from its abundant occurrence in the vicinity of that city, and FreeStone, or Oolite, of which Portland Stone is a notorious variety. There then commonly occur various Sandstones, with veins of Chert and Oxides of Iron; and lastly we arrive at Chalk, and superincumbent Alluvial matter." Of all these we must speak in order. But in referring to a variety of books, in order to extract from them what may be most suitable to your progress, I find some difficulty in determining what order should be now observed, every work differing in some degree from others in the arrangement, though not contradicting each other in effect. It is not of very much consequence which of these substances we place first; since they do not, as I have already told you, occur regularly one above another every where, but some in one part of the country and some in another, though when together tolerably regular in position: I must only beg, that if, in the first geological book you open, you find that first which I have placed second, you will not hastily conclude that I have taught you wrong. We will speak first of what is called the New Red Sandstone, Red Rock, Red Ground, or Red Marle, for all these names are given to it by different writers. It is a very extensive deposit. Its texture is very various. It appears sometimes as a reddish Marle or Clay, sometimes as a Sandstone; sometimes the Clay and Sandstone are interstratified or pass the one into the other; and it will further appear that it is associated with, or contains beds of a conglomerate, consisting of masses of different rocks cemented by Marle or by Sand. When this deposit appears as a Sandstone, its characters differ greatly in different places; it was occasionally calcareous, and sometimes of a slaty texture. Above all, this extensive deposit is remarkable for containing masses or beds of Gypsum, and the great Rock-Salt formation of England ocuurs within it, or is subordinate to it; in some places the Coal Strata dip beneath it."

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Fig. 2.

GEOLOGY.

Fig.3.

Fig.4.

Pub by Baker & Fletcher, 18, Finsbury Place.

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MAT.-I thought you had mentioned the Salt mines as occurring in the Old Red Sandstone.

MRS. L.-I did so-because I found it so stated in the works I was there quoting, and I thought it better to speak of these substances where they were stated to occur. I imagine there is no contradiction in the fact-but that either they occur in both the Old and New Red Sandstones, or that the Red Marle, a particular sort of Sandstone in which they are found, is by some Geologists ranked with the former, and by some with the latter. If you bear this in mind, and remember what we said of those substances, no confusion will arise, and we may proceed with our present subject. "The Marle and Sandstone are often red, but vary in their hue from chocolate to salmon colour; they are not unfrequently variegated, exhibiting streaks of light blue or verdigris, buff or cream colour. This is called variegated Sandstone. At Westbury, on the Severn, in Gloucestershire, it is for the most part greyish blue, and chocolate red, alternating at intervals of about a foot, but sometimes crossing each other, and sometimes intermixed. The soil of Marlborough is so red, that the butchers at Dodbrook market know the sheep that come from thence by the colour of the fleece." From the prevalence of this colour in the soil, many places have their names-as Rougemont Castle in Exeter, Radford, Red-hill, and Ratcliff in Somersetshire, Retford in Derbyshire, &c. Fullers' Earth is raised from the Marle beds in Yorkshire.

ANNE. I have often heard of Fuller's Earth, but have not a distinct idea what it is.

MRS. L.-It is one of the Soap Stones, so called from a sort of greasy feel like Soap, and answering in some degree the purpose for which Soap is used. Fullers' Earth has a greenish-grey colour, and a dull earthy appearance-it falls to powder in water, and is much used for cleansing different articles. Fig. 4 is a specimen. "The Rock of which we were speaking is generally unfit for architectural purposes, but in some

places has sufficient cohesion to afford some of the finest Freestone in the kingdom. The tower of Shenton, in Devonshire, is a proof that sometimes it is durable. In the parish of Addington, Cumberland, the Druidical temple, called Long Meg and her daughters, consists of Red Grit-stone; some of the stones are eighteen feet in height, and seventeen girth. "From the softness of this Sandstone it has often been excavated into extensive caverns; such as those near Nottingham, which, as they gave rise to the name of the place, Snowdengaham, "the home of caverns," must have formed the dwellings of the rude aborigines: there are similar, but smaller excavations at Knaresborough, and at Guy's Cliff in Warwickshire." No organic remains are said to be found in this rock.

ANNE. I see the term Lias frequently used in some books I have been looking into, and I think you once named it without explanation.

MRS. L.-It is a common term for a formation of Limestone, called sometimes Upper Limestone, in distinction from that I have described to you, which is called Lower Limestone; at other times, Argillaceous Limestone, being much mixed with clay. This Lias Limestone is particularly characterised by its dull, earthy aspect: in colour it varies in different beds from light slate blue or smoke grey, to white. The Blue Lias, which contains much Iron, affords a strong Lime. The White Lias takes a high polish, and may readily be employed for the purposes of Lithography. It must however be distinguished from the stone generally so applied on the continent, which is brought from the quarries of Solenhofen, and is of much more recent formation. The Lias is never variegated in colour like common Marble, nor brecciated, nor does it admit of brilliancy or depth of tint, but it occasionally exhibits dentritical appearances, as the Cottam Stone Marble. Some irregular beds consist of what are called Cement Stones, because used in making Parker's Cement. The Cement Stones are of different

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