AND OF THE PHYSICAL SCIENCES. 



163 



slate and gnei=s-slate, however, bold a station quite apart from the others, and are cer- 

 tainly altogether distinct. On the other hand, clay-elate (used in a limited sense), roof- 

 ing-slate, dunstone, and greywacke-slate, are observed to pass gradually into one another, 

 and to reciprocate each other's qualities. Again, greywacke-slate, flinty-slate, Lydian- 

 stone, (?) and greywacke, graduate into one another. Roofing-slate is found sparingly, 

 and in small patches. It obviously passes into the general mass of clay-slate, of which, 

 notwithstanding its containing oiganic remains, I have above surmised that it may in 

 propriety be ranked apart. The general body of clay-slate as?umes a great variety of 

 aspects, which are manifestly graduated, sometimes approximating the typical roofing- 

 slate, and sometimes degenerating into a loose brown debris, or becoming indented, 

 or closely impacted, constituting *' dunstone ;" not unfrequently also running into 

 decided greywacke, either in small patches, or even in extensive beds. Altogether, 

 these last named rocks form the generality of our hills which are round backed. In 

 situations where the slate i<i in tolerably-sized fragments, fo'isils are found in plenty. 

 Greywacke, flinty-slate, and Lydian-stone ? are found In one situation, in close ap- 

 proximation to greywacke-slate, this last being itself the staple rock of that spot, 

 and passing with great freedom into greywacke, and rather less so into the others. 

 It and the flintj'-slate are fossiliferous. Although I have mentioned certain kinds of 

 slate as being fossiliferous, I believe that no fixed rule can be laid down on this sub- 

 ject, for the same kind of slate will in one place exhibit these remaining, and in 

 another be destitute of them. Greywacke-slate is most constant in this respect. 

 The rubbly and loose kinds of clay-slate, and the best kinds of roofing- slate, seldom 

 contain ihera. The generality of our slate, that, namely, to which I presume the term 

 clay-slate may be applied, is found assuming for the most part the appearance of small 

 and loosely joined fragments of a light-grey colour, sometimes blueish-grey, much 

 tinged with iron, and frequently intersected hy seams of quartz. At intervals, these 

 hills of clay-slate give good quarries of roofing-slate, of a bright lead colour, in which 

 fossils are freely distributed. These quarries are in general soon worked out, the 

 stone soon becoming dense with greywacke, or degenerating into a rubbly state, or a 

 dunstone, which is an indurated form of clay-slate. The course and dip of our slate 

 vary greatly, even at times within a small space. I have understood that near Exeter 

 is a bed of slate horizontal in its course. Thi^, it was thought, was a rare circum- 

 stance, but in this neighbourhood it is far from being an uncommon appearance, 

 though only observed in small patches. From a level it varies to a close approxima- 

 tion to verticality. It faces usually from about south-west to about south-east, but 

 likewise at times looks southwardly, eastwardly, and westwardly, or thereabouts ; but 

 though it is thus prone to variation, even repeatedly within a small distance, I am not 

 aware that it ever faces northwardly of ea?t and west. Its solidity varies sometimes 

 within very confined limits, and this often depends on the sudden presence of Grey- 

 wacke, which is seen to pervade the slate with great freedom in some spots. At 

 times there is reason to believe that access of air determines the decomposition of 

 slate, though in the cases where this is supposed to have happened, I should consider 

 from its brown and powdery appearance, that some peculiarity of chemical composition 

 had existed previously. Generally, however, the loose rubbly condition in which we 

 observe a deal of our slate to exist, cannot have been owing, at least in the first in- 

 stance, and principally, to atmospheric influences ; for in some places, as at the slate 

 quarries, this presumed decomposition shews itself throughout the whole depth to 

 which the rock has been worked — at one spot the rubbly and loose state of the rock 

 gradually disappearing, and the substance by degrees getting closer, until it is fairly of 

 the character of dunstone, or at the least of ordinary slate. Indeed, this transition 

 from loose to indurated slate is exemplified most freely in this neighbourhood, and 

 seems to be inconsistent with a supposition of decay from the agency of air. The 

 oxide of iron occasionally stains our slate in fantastic shapes. It seems also to occur 

 m greatest plenty in the immediate neighbourhood of fossils, and in their composition. 

 I occasionally find fragments of slate in the quarries on which are marked dark, broad, 

 concentric lines, in the manner of the layers of wood in the boles of trees, of which 

 appearances I can offer no explanation. There is one fact in the history of our slate 

 worthy of notice, and worthy of being further investigated with a view to some ex- 

 planation. This is the bendings or reflexions in the slope of the rock observed in 

 very many places. In one spot in particular I have observed it to be bent four times 

 in the depth of as many feet, so as to assume a perfectly zig-zag appearance. It 

 must be recollected that this occurrence is not limited to loose and disconnected kinds 

 of slate, but may be seen on larger scales in good solid sorts also, though the repeated 

 reflexions may not be here so remarkable or perfect. At Crab-Tree, near Plymouth, 

 there is a hill .of slate, which towards its summit turns off at an obtuse angle, which 

 gives this rock a peculiar aspect. Mr Hennah, in a work before named, records an 

 instance where the slate seems as if thrust up by some violent impulse from below, 

 between two beds of hme. I am of opinion that several similar instances, as regards 

 this appearance of the rock, can be shown in our neighbourhood, though as to the 

 cause of this, as well as of the reflexions above specified, I can offer no satisfactory 

 notion. 



Greywacke-slate assumes a very different appearance from all others. It is harder, 

 and not so extensively tabular, is of a dark lead colour, and passes very freely, and 

 very suddenly, into greywacke, at numerous points. Viewing it as it appears on the 

 coasts, it displays itself in large flat cakes, having thin and rounded edges between 

 which other cakes are in their turns inserted. It passes also with freedom into flinty- 

 slate, and also I suspect into Lydian-stone, but here I want the opinion of some com- 

 petent judge. In the flinty-slate are found the turbinolias formerly alluded to. Be- 

 neath the water these are dislodged by the action of that element from their bed, and 

 thrown up in more or less perfection of form on the beach, afact corroboraiive of the 

 general rule of fossils exceeding in density the matrix in which they occur. Dr 

 Leach reports that at Buckfast in this connty the lime is seen covering the slate, and 

 that they both at this spot contain a quantity of flinty matter. Now, it is singular 

 that close to the place where I reside, there is seen a small quantity of lime ore^rlaid 

 by the slate, and both containing flinty matter !—a fact seemingly confirming amongst 

 ot ers before named, the contemporaneous deposition of these strata, or at least their 

 close relationship with respect to the convulsions which have disturbed the crust of 

 oar globe. The circumstance of strata at their points of junction being more or less 



cemented, |blcnded together, and intermixed, appears to me to have attracted trvo 

 little notice, for though in some cases their admixture seems rationally accounted for 

 by the previous well-founded conjeeiuro, that their deposition was coeval, there are 

 other instances in \^hich we have no ground for imagining that their depositions wore 

 coetaneous. Lime and slate are most freely intermixed at their points of junction ; 

 and we see the same thing occurring between the slate and sandstune in spots where 

 these meet, the latter frequently behig wedged into the other; and in some places 

 there being a union of qualities. But then, there are other reasons for imagining the 

 contemporaneousness in the deposit of these strata. On the other hand, where slate 

 abuts against granite or trap, we fi::d that in some spots the former is cemented 

 freely to the latter. This is seen ii: numerous blocks scattered profusely through the 

 valley at Joybridge, but I am not fi nsible of any cases where there is a thorough in- 

 termixture, as seen between slate and limestone. 



Amongst the varied relations assumed by slate in its before named general diffusion, 

 there is one which seems to indicate that even the oldest (allowing for argument that 

 they are of different ages) kinds of slate were not contemporary with granite, for this 

 rock not only extends into contact with granite at our north, but even spreads be- 

 tween the hills of that primitive formation, assuming, I presume, in its run a length- 

 ened three-sided figure. Whatever be the actual relations between lime and slate (or 

 at least certain sorts of the latter), and whatever may be the depth to which the lime 

 as a whole, or in some parts, descends, I must not omit to furnish an additional proof 

 of the intimate connexion subsisting between these two strata, namely, that " Lime 

 appears in masses on the north, south, and west sides of the Dart, insulated in schistus." 

 (Carrington's Dartmoor, Preface.) 



The most common fossils in our slate are the encrinites, of which there seem to 

 be several species, and all different from those in the limestone. Perhaps ihe next 

 kind most generally diffused is a sort of coral, or rather, more properly certain species 

 of corallites, for the specimens differ very greatly. One which I have is thick, sepa- 

 rate, and fan-shaped; another is fixed in relief, and of a loose powdery texture ; while 

 a third sort is like the last alseform, and appears as a mere impression in roofing-slate. 

 They are all small in size. The turbinolias seem limited to the flinly-slate at Bovi- 

 sand, but are there most plentiful. My brother procured from the slate at Crah-tree 

 a species of '* trilobus." Madrepores are found, though rarely, in slate. They seem 

 to be very similar to, if not identical with, those so common in lime. In the flinty- 

 slate at Bovisand, Miss Hook has found two anomalous specimens. One has the ap- 

 pearance of a Turbo, and the other bears a considerable similarity to a crab; but 

 these are highly ambiguous. There are also various other fossils, of which I can ren- 

 der no definite account. 



Decomposed and comminuted slate from old building'i, is used with benefit as a man- 

 ure, for besides acting mechanically in separating tenacious clots of soil with which 

 we may combine rt, it? composition shews that it is no despicable ingredient, of a pro- 

 ductive soil. Shoemakers use what I conceive to be Lydian stone as " lap-stones," 

 they being found on the shore of the required rounded shape, and possessing great 

 density and tenacity. 



VARIETIES. 



Instinct of Animals. — The following curious statement is copied from a letter 

 which the late William Fischbein, the well known animal painter, wrote in explana- 

 tion of one of his most beautiful coloured sketches, now in possession of M. Meyer, 

 of Hildburghausen. It represents five little red mice, in the presence of a young cat. 

 ** That instinct is an inherent or innate quality of animals, is clearly proved by ex- 

 perience. The cat possesses the instinct of catching and eating mice, and the mouse 

 that of shunning the cat as its most dangerous enemy. Once, in Rome, I happened to 

 open a drawer which 1 seldom had occasion to use, when I saw a mouse jumping out 

 of it, and found among the papers a nest with five young mice, naked and blind, and 

 of a pale flesh colour. I placed them on a table, handled them, Stc, and they evinced 

 no sjTnptoms of fright, nor any inclination to get away, but only appeared eager to 

 approach each other for the sake of warmth. There happened to be in the house a 

 very young cat, which had never tasted anything but milk. I placed it near the 

 little mice, by way of experiment, but to my astonishment it did not even look at 

 them, nor perceive them, even when 1 turned its eyes in the proper direction, until 

 at last, when I had repeatedly approached its nose to the mice, it suddenly caught a 

 scent which made it tremble with desire. The propensity became more and more 

 violent, and the cat smelled at the mice, touching them with its nose, when all at 

 once, the pale-coloujed like creatures became suffused with blood, and began to make 

 great exertions to get out of the way of imminent danger, whilst the cat as eagerly 

 followed them." — Dr tfeissenborn^ in Mag. of Nat. Hist. 



The Vampire Bat of South Ajierica is often the cause of much trouble by 

 biting the Horses on their withers. The injury is generally not so much owing to 

 the loss of blood, as to the inflammation which the pressure of the saddle afterwards 

 produces. The whole circumstance has lately been doubted in England ; I was there- 

 fore fortunate in being present when one was actually caught on a horse s back. We 

 were bivouacking late one evening near Coquirobo in Chile, when my servant, noticing 

 that one of the horses was very restive, went to see what was the matter, and fancy- 

 ing that he could distinguish something, suddenly put his hand on the beast's withers 

 and secured the Vampire. In the morning, the spot where the bite had been inflicted 

 was easily distinguished, being slightly swollen and bloody. The third day afterw*ards we 

 rode the horse without any ill effects. Before the introduction of the domesticated 

 quadrupeds, this Vampire Bat probably preyed on the Guanaco or Vicugna, for these, 

 together with the Puma and Man, were the only terrestrial Mammaha <if large size 

 which formerly inhabited the Northern part of Chile. — Darwiriy in the Zoology of 

 the Voyage of H. M. S. Beagle, 



Preservation of Corn. — Thinking that all granaries are but imperfect shelt'^r 

 from the vicissitudes of weather, General Demarcay has made use of an ice-house si- 

 tuated on his estate, but no longer used as such. Its depth was sufficient to render 

 it impervious to atmospherical changes, and he lined it with wooden planks so as to form 

 a large case, but which was at some little distance from the bottom and the sides of 



