REVIEWS AND NOTICES OF BOOKS.

Acadian Geology and a Supplementary Chapter thereto*.

The first of the works mentioned in the note at the foot of this page contains the only comprehensive account yet published of the highly interesting and difficult geology of Nova Scotia and the neighbouring regions. This book is too widely known to the geologists of all countries to need any critical examination at the present time. Since its publication the author has removed from the field of his former labours among the carboniferous and New Red sandstone works of Nova Scotia, to the great Silurian plain of Lower Canada. He still labours (as we hope he may long continue to do) to " carry forward" to completion some of the subjects left unfinished in 1855. The results, up to the present time are now published is a neat pamphlet with the title of "Supplementary Chapter to Acadian Geology." It contains a series of condensed articles giving us the recent discoveries and investigations of the author on various points connected with the geology of the Acadian Provinces, such as the Modern and Post Pliocene formations, and the minerals and fossils of the carboniferous, Devonian and Silurian rocks. We extract an account of some investigations made by Professor How.

"Professor How's paper announces the discovery, in the great bed of gypsum quarried at Windsor, of a rare boracic-acid mineral hitherto found only in Peru. Its formula, according to Professor How, is

Na O 2 BO, + 2 Ca O, 3 B 0, + 15 H O.

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"With respect to the geological conditions of its occurrence, Professor How quotes from Professor Anderson of Glasgow the

1. ACADIAN GEOLOGY.-An account of the Geological Structure and mineral resources of Nova Scotia and portions of the neighbouring Provinces of British North America. Edinburgh, 1855, 8vo., with a map and illustrations.

2. SUPPLEMENTARY CHAPTER TO ACADIAN GEOLOGY.-12mo. pp. 70. Wood engravings of fossils. By Dr. J. W. Dawson, LL.D., F.G.S. Principal of McGill College, Montreal. Author of Archaia, &c. Edinburgh, 1860.

† Professor How has still more recently discovered a second boracicacid mineral in the gypsum. It consists of borate and sulphate of lime, soda, and magnesia, and Professor H. proposes to name it Cryptomorphite.

statement that, at Tarapaca in Peru, the mineral is found in a district supposed to be volcanic, and imbedded in the nitrate of soda deposits. He then remarks that, with a very few exceptions, boracic acid is found either in directly volcanic regions, most abundantly as such, or as borax: and a well-marked case of actual sublimation of the acid from a volcano in the island of Vulcano, near Sicily, has been studied by Warrington; or in smaller amount, in minerals the products of recent or extinct volcanoes, as Humboldtite from ejected blocks of Vesuvius, and zeolites and datholite from trap of Salisbury Crags, New Jersey, and other places; or in minerals of purely plutonic or metamorphic rocks, as tourmaline, the rhodozite of Roze, and axinite-the species which contain it at all being few in number. It may be noticed also, that traces of this acid have lately been met with in the Kochbrunnen of Wiesbaden and in the waters of Aachen.

"If we may reason from the character of the majority of its situations, we may almost consider the volcanic or at least igneous origin of boracic acid so well established as to lead us, by its occurrence in the gypsiferous strata, to seek for some volcanic agency as the cause of their production. Such an origin has I find already been assigned to the gypsum of Nova Scotia by Mr. Dawson. This formation has been shown to be a member of the Lower Carboniferous series, and is assumed to have arisen from the action of rivers of sulphuric acid more or less dilute, such as are known to exist in various parts of the world, issuing from then active volcanoes and flowing over the calcareous reefs and bed of the sea.

"This is an interesting confirmation of the views formerly expressed as to the origin of the gypsum; and though Professor Hunt has ably shown, in his recent papers on Chemical Geology, that gypsum may be produced in stratified masses in aqueous deposits by other processes, I am still inclined, in consequence of the great thickness and local character of the deposits, and the apparent absence of magnesian limestone, as well as the presence of boracic acid, to adhere to the view above stated, in so far as the great gypsum beds of Nova Scotia are concerned."

The following are some of the results of Dr. Dawson's re

Report of Canadian Survey for 1858; Canadian Naturalist; Silliman's Journal, &e.

searches into the origin and composition of the "mineral charcoal," and "compact coal" of the carboniferous system.

"A consideration of the decay of vegetable matter in modern swamps and forests shows that all kinds of tissues are not under ordinary circumstances susceptible of the sort of carbonization which we find in the mineral charcoal. Succulent and lax parenchymatous tissues decay too rapidly and completely. The bark of trees very long resists decay, and, where any deposition is proceeding, is likely to be imbedded unchanged. It is the woody structure, and especially the harder and more durable wood, that, becoming carbonized and splitting along the medullary rays and lines of growth, affords such fragments as those which we find scattered over the surfaces of the coal. These facts would lead us to infer that mineral charcoal represents the woody debris of trees subjected to subaerial decay, and that the bark of these trees should appear as compact coal along with such woody or herbaceous matters as might be imbedded or submerged before decay had time to take place.

"The method of preparing the mineral charcoal for examination was an improvement on the "nitric-acid " process of previous observers, and the results gave very perfect examples of the discbearing tissue restricted in the modern world to conifers and cycads, but which existed also in the Sigillariæ of the coal period. With this were scalariform vessels, like those of ferns and club mosses, and several other kinds of woody tissue. On careful comparison it was found that all these tissues might be referred to the following genera of plants common in the coal measures: Sigillaria including Stigmaria, Calamites, Dadoxylon and other conifers, Lepidodendron, Ulodendron, ferns, and possibly some other less known plants.

"Another form of tissue observed was a large spiral vessel, possibly belonging to some endogenous plant.

"The structures preserved in the layers of shining compact coal are more obscure, and I therefore present a somewhat more full summary of the facts known in respect to them :—

"The compact coal, constituting a far larger proportion of the mass than the "mineral charcoal" does, consists either of lustrous conchoidal cherry or pitch coal,-of less lustrous slate coal, with flat fracture,-or of coarse coal, containing much earthy matter. All of these are arranged in thin interrupted laminæ. They consist of vegetable matter which has not been altered by subae

rial decay, but which has undergone the bituminous putrefaction, and has thereby been resolved into a nearly homogeneous mass, which still, however, retains traces of structure and of the forms of the individual flattened plants composing it. As these last are sometimes more distinct than the minute structures, and are necessary for their comprehension, I shall, under the following heads notice both as I have observed them in the coals in question.

"1. The lamina of pitch or cherry coal, when carefully traced over the surfaces of accumulation, are found to present the outline of flattened trunks. This is also true, to a certain extent, of the finer varieties of slate coal; but the coarse coal appears to consist of extensive laminae of disintegrated vegetable matter mixed with mud.

"2. When the coal (especially the more shaly varieties) is held obliquely under a strong light, in the manner recommended by Goeppert, the surfaces of the lamina present the forms of many well-known coal-plants, as Sigillaria, Stigmaria, Poacites or Cordaites, Lepidodendron, Ulodendron, and rough bark, perhaps of conifers.

"3. When the coal is traced upward into the roof-shales, we often find the lamina of compact coal represented by flattened coaly trunks and leaves, now rendered distinet by being separated by clay.

"4. In these flattened trunks it is the outer cortical layer that alone constitutes the coal. This is very manifest when the upper and under bark are separated by a film of clay or of mineral charcoal, occupying the place of the wood. In this condition the bark of a large Sigillaria gives only one or two lines in thickness of coal; Stigmaria, Lepidodendron, and Ulodendron give still less. In the shales these flattened trunks are often so crushed together that it is difficult to separate them. In the coal they are, so to speak, fused into a homogeneous mass.

"5. The phenomena of erect forests explain, to some extent, the manner in which layers of compact coal and mineral charcoal may result from the accumulation of trunks of trees in situ. In the sections at the south Joggins, the usual state of preservation of erect Sigillariæ is that of casts in sandstone, enclosed by a thin layer of bark converted into compact, caking, bituminous coal, while the remains of the woody matter may be found in the bottom of the cast in the state of mineral charcoal. In other cases the bark has fallen in, and all that remains to indicate the place

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of a tree is a little pile of mineral charcoal, with strips of bark converted into compact coal. Lastly, a series of such remains of tumps, with flattened bark of prostrate trunks, may constitute as rudimentary bed of coal, many of which exists in the Joggins section. In short, a single trunk of Sigillaria in an erect forest presents an epitome of a coal-seam. Its roots represent the Stigmaria underclay; its bark the compact coal; its woody axis the mineral charcoal; its fallen leaves, with remains of herbaceous plants growing in its shade, mixed with a little earthy matter, the layers of coarse coal. The condition the durable outer bark of erect trees concurs with the chemical theory of coal, in showing the especial suitableness of this kind of tissue for the production of the purer compact coals. It is also probable that the comparative impermeability of bark to mineral infiltration is of importance in this respect, enabling this material to remain unaffected by causes which have filled those layers consisting of herbaceous materials and decayed wood, with earthy matter, pyrites, &c.

"6. The miscroscopic structure of the purer varieties of compact coal accords with that of the bark of Sigillaria. The compact coals are capable of affording very little true structure. Their cell-walls have been pressed close together; and pseudo-cellular structures have arisen from molecular action and the segregation of bituminous matter. Most of the structures which have been figured by microscopists are of this last character, or at the utmost are cell-structures masked by concretionary action, pressure, and decay. Hutton, however, appears to have ascertained a truly cellular tissue in this kind of coal. Goeppert also has figured pa renchymatous and perhaps bast-tissues obtained from its incinera. tion. By acting on it with nitric acid, I have found that the structures remaining both in the lustrous compact coals and in the bark of Sigillariæ are parenchymatous cells and fibrous cells, probably bast-fibres.

"7. I by no means desire to maintain that all portions of the coal-seams not in the state of mineral charcoal consist of cortical tissnes. Quantities of herbaceous plants, leaves, &c, are also present, especially in the coarser coals; and some small seams appear to consist entirely of such material,-for instance, of the leaves of Cordaites or Poacites. I would also observe that, though in the roof-shales and other associated beds it is usually only the cortical layer of trees that appears as compact bituminous