or hornstone, but also scraps of bluish argillite in a clayey cement, and of this there is often no more than is barely suf ficient to hold the grains together, sometimes with and sometimes without mica, commonly compact, sometimes slaty in the gross."

Humboldt applies the term grau wacké to the arenaceous transition rocks, which contain only small fragments of simple substances, more or less rounded, but not to those containing fragments of composed rocks.

It is evident that the rock which holds so conspicuous a place in the geological structure of the vicinity of Boston, is not simple wacké, or the compound rock grau wacké. Neither is it the rock known in Europe by the name of "Plumpudding stone," which is wholly composed of flint pebbles, cemented by flint. The appropriate name for our rock is Conglomerate.

After describing grau wacké as already quoted, Prof. Jameson remarks, that another rock is occasionally met with in transition districts, and is named "transition conglomerate." It is composed of rounded or angular masses of granite, porphyry, gneiss, and clay-slate, often larger than a man's head." The term conglomerate is applied only to those compound rocks containing large fragments of rocks which have been usually called primitive. This conglomerate passes into coarse grau wacké, fine grained grau wacké, and grau wacké slate, which becomes at last distinct clay slate. All these transitions are seen in the neighbourhood of this town, especially at Roxbury, Brookline, and Brighton. The nature of this rock, and the propriety of the name given it, will be evident from an enumeration of the substances entering into its composition. They are as follows:

Hornstone, of a brick red colour, flesh red and purple: also, green of different shades.

Quartz, of different shades of grey, rarely snow-white, sometimes ferruginous.

Compact Felspar, green, light red, brown and

grey.

Flinty Slate, passing to Lydian stone, grey and black. Porphyry, having a base of compact felspar approaching to hornstone; the imbedded crystals of felspar are of a red colour of different shades; it also embraces crystalline grains of quartz.

Granite, the felspar of which is nearly flesh red, the quartz and mica brown.

Clay Slate, greyish blue, sometimes light ash colour; it

has more or less of an earthy aspect, and emits an argillaceous odour.

Novaculite, of a grey colour.

Serpentine, in small quantity, in various parts of the bed; it has a light green colour, and is soft.

Nephrite, of a greenish white colour, sometimes greyish

white.

These materials are present in the rock in various proportions; the hornstone, compact felspar, and quartz, being the most abundant. The masses vary in size, from that of a pea, or even smaller, to that of several feet in diameter. They are not angular fragments, but rounded, and ovoidal, and are connected by a cement apparently composed of the same materials in a more or less comminuted state. The nodules often project from the natural sections of the rock, in bold relief; in other cases they are absolutely flat, as if cut through by a sharp tool. This last appearance is especially observable where fissures exist in the bed, and these fissures are exceedingly numerous, and of great extent. In some places they are of considerable width; in others they are scarcely discernable, the opposite surfaces of the rock being still in close contact. Wherever these fissures occur, the nodules, whatever may be their size, are completely divided, and the corresponding surfaces are directly opposed to each other; no appearance of subsidence of those on one side, or elevation of those on the other can be discovered.

An interesting question here presents itself.

In what manner are we to account for the occurrence of these fissures? Can it be explained on the known laws of crystallization? Our reply must be in the negative. In those well known instances of the separation of a crystal into two parts, where the two portions are seen at some distance apart, the connexion is preserved by the intervention of a layer of the matrix, or of one of its component parts, but in the case before us there is not a particle of any of the component parts of the rock interposed; the two opposing surfaces are completely detached. It cannot be imagined that the particles arranged themselves round any centre of crystallization common to the two. The two cases are far from being analogous.

That the fissures are not the effect of violence, the invasion, for example, of any other rock in a state of fusion, amongst the imbedded nodules, is equally evident. Had this been the case, we should unquestionably find in some parts of the bed, if not in all, elevations, depressions, and contortions, on the

opposite sides of the fissures, of which there are not the slightest vestiges. Neither can we refer it to subsidence of the strata, which would have changed the relative position of the separated parts.

Should it be conjectured that these nodules once constituted an accumulation of diluvial pebbles, which were enveloped in a fused mass, by which they were irregularly heated and split, why, it may be asked, was not every pebble similarly affected, and split in many directions? We find them divided only in one direction.

Again it may be urged that the whole was in a state of semifusion, and suddenly cooled, which, as we know in other cases, produces rents and fissures; to this mode of explanation the same objections apply as in the last case.

From observing cracks and fissures on the surface of clay and mud which has been rapidly deprived of moisture, some geologists have resorted to dessication to account for the seamed structure of rocks. But if these cracks and fissures be carefully examined, they will be found to diminish in width as they descend, being much wider at the surface than at a short distance below it. No such appearance is observable in this conglomerate; the fissures, whatever may be their width, continue undeviatingly the same as far as they can be traced, and this is a very considerable distance on the sides of the beds, and in the quarries which are worked.

Some may conceive that these fissures are to be attributed to the operation of earthquakes, and at first sight this would seem the most plausible hypothesis. There is, however, one fact which should lead us to doubt whether such a supposition would be satisfactory. On examining the fractured surfaces of the enormous masses of this rock, which are so frequently separated by the aid of gunpowder,* we find them broken, rough, and irregular, never presenting that smoothness 80 uniformly seen in the natural fissures. Had the latter been produced by earthquakes, they would in all probability have presented, in a still more conspicuous manner, an appearance similar to that resulting from the action of the less powerful

agent.

We are yet, it is to be feared, in want of a theory capable

• Portions of this rock thrown off by blasting are often of astonishing size; and to effect this, advantage is taken of the numerous fissures, which are more or less filled with gunpowder, thirty or more pounds of it being distributed in them; the whole is then exploded, and enormous masses are thrown off.

of solving this, and many other circumstances in the structure and present appearance of rocks, which the activity of geologists is almost daily bringing to light. But although we should find difficulties of this kind increasing upon us as our researches extend, far from discouraging us in the pursuit, they should be viewed as additional incentives to exertion. "It is among difficult and unexplained phenomena," as has been so strikingly illustrated by the labours of Dr Macculloch, whose words I quote, "that we are to seek for the stimulus which will lead us to pursue those researches, on the multiplication of which alone we can hope to found a true system; and it is to a salutary distrust of the all-sufficiency of any hypothesis, that we must look for protection from its paralyzing influence."

[To be continued.]

General Intelligence.

Iodous Acid.-Il Sig. Sementini, of Naples, has published an account of a combination of iodine and oxygen, containing less of the latter principle than iodic acid. It is obtained in the following manner:-equal parts of chlorate of potassa and iodine are to be triturated together, in a glass or porcelain mortar, until they form a very fine pulverulent yellow mass, in which the metallic aspect of the iodine has entirely disappeared. If there be excess of iodine, the mixture will have a lead colour. This mixture is to be put into a retort, the neck being preserved clean, and a receiver is to be attached with a tube passing to the pneumatic trough. Heat is then to be applied, and for this purpose a spirit-lamp will be found sufficient; at first a few violet vapours rise, but as soon as the chlorate begins to lose oxygen dense yellow fumes will appear, which will be condensed in the neck of the retort into a yellow liquid, and run in drops into the receiver; oxygen gas will at the same time come over. When the vapour ceases to rise, the process is finished, and the iodous acid obtained will have the following properties:

Its colour is yellow; its taste acid and astringent, and leaving a burning sensation on the tongue. It is of an oily consistency, and flows with difficulty. It is heavier than water, sinking in it. It has a particular odour, disagreeable, and

something resembling that of euchlorine. It permanently reddens vegetable blues, but does not destroy them as chloric acid does. It is very soluble in water and alcohol, producing amber-coloured solutions. It evaporates slowly, and entirely in the air. At 112° F. it volatilizes rapidly, forming the dense vapour before mentioned. It is decomposed by sulphur, disengaging a little heat, and liberating violet vapours. Carbon has no action on it at any temperature; solution of sulphurous acid decomposes it as well as iodic acid, precipitating the iodine as a brown powder. a brown powder. It is characterized by the manner in which potassium and phosphorus act on it; the instant they touch it they inflame; the potassium producing a white flame and dense vapours, but little or no liberation of iodine; and the phosphorus, with a noise as of ebullition, violet vapours appearing at the same time.

The odorous nature of this acid, its volatility, colour, and its power of inflaming phosphorus by mere contact, shew that some of the principal characters of iodine are retained, and that it is oxygenated, therefore, in a minor degree, and deserves the name of iodous acid.

Its composition has not been experimentally ascertained. M. Sementini endeavoured to analyze it by putting 100 grains into the end of a long sealed tube, and then dropping a small piece of phosphorus in, iodine was disengaged, and condensed in the upper part of the tube, and this was found to amount to 45 grains but this can furnish only very uncertain results. Jodous acid dissolves iodine, becoming of a deep colour, more dense and tenacious, and having more strongly the odour of iodine when heated, the iodine partially rises from the iodous acid, but they cannot be separated in this way.

M. Sementini believes also in an oxide of iodine, and has given the name to the black powder, which is produced by the action of sulphurous acid or iodous acid, and which still contains oxygen; but he mentions that this and some other points still require investigation.

The following are the properties of the iodic and iodous acids, by which a judgment may be formed of their specific difference. Iodic acid is solid, white, without odour, reddening blue colours, and then destroying them. Volatile at 456° F., with decomposition: heated with charcoal or sulphur, it is decomposed with detonation. Iodous acid is liquid, yellow, odorous, reddening blue colours, but not destroying them; volatilizing at 112° F., and even at common temperatures without decomposition; heated with sulphur, it is decomposed