Observations on the Lakes of Canada, &c.-In a memoir read at a meeting of the Geological Society of London, April 23d, by Lieutenant Portlock, R. E. the author described the various nature of the shore, of Lakes Huron, Michigan, Erie, and the other lakes of Canada, and annexed a plan, in which a tabular view was presented of the comparative level of these lakes and their communications with each other. At the falls of Niagara, he observes, the upper stratum is a firm compact limestone, resting on strata of a very schistose nature. It is not by erosion of the surface, that the falls are made to recede, but the waters after falling one-hundred and fifty feet, strike the bottom, and are reduced to foam; they are then driven up into the air far above the rock whence they had descended; this penetrating foam acts on the lower argillaceous strata, till the overhanging rock is undermined. Lieutenant Portlock remarks, that there has been a gradual fall in the level of the lakes at Canada.-[Ann. Philos.]

New Locality of Apatite. I have lately found this mineral in considerable abundance at Billerica, in Massachusetts. It occurs about two miles beyond the meeting-house, on the western bank of Concord river, in a coarse granite, the felspar of which is of a beautiful flesh red colour, and in concretions of very great size. This granite appears to be a vein, and the apatite, which is the conchoidal variety, the asparagusstone, is in distinct crystals, which are six-sided prisms truncated on the lateral edges. It is probable that this will be found to be the richest locality of this beautiful mineral, as yet discovered in the United States.

Arsenical iron and Galena have been met with, in small quantity, in veins of quartz traversing granite and gneiss, at Dunstable on the river Nashua. Tourmalin and garnets occur at both these localities. J. W. W.

ERRATA.

In Vol I.page 586, 8th line from the bottom, for 9 read 12.7

7th

2d

3240 2,015,000

1

4572 285,750

.14

THE

Boston Journal

OF

PHILOSOPHY AND THE ARTS.

ART. I.-On Rock Formations. By BARON ALEXANDER HUMBOLDT. [Edin. Jour.]

[Concluded from page 21.]

FROM that scepticism which would deny the existence of any kind of regular order in the position of rocks, it is proper to distinguish an opinion which has sometimes found supporters among experienced observers. According to this opinion, the formations of gneiss-granite, of greywacke, of alpine limestone, and of chalk, which have a uniform superposition in different countries, do not very well correspond among themselves as to the age of the homonymous elements of each series. It is thought that a secondary rock may have been formed on one spot of the globe, while transition rocks did not yet exist on another spot. In this supposition, no allusion is is had to those granitic rocks which are found lying above limestone containing orthoceratites, and which are consequently newer than the primitive rocks. It is a fact generally admitted at this day, that formations of analogous composition have been repeatedly deposited at epochs far removed from each other. The doubt which we are now considering, (though we do not partake in it), bears on a point much less clearly established,the ascertaining whether certain mica-slate rocks, evidently situated in the midst of a country of primitive rocks, and

VOL. II. NO. II.

14

placed below those in which the vestiges of organic life begin to appear, are newer than the secondary rocks of another country. I confess, that, in the part of the globe which I have had an opportunity of examining, I have not seen any thing that might tend to confirm this opinion. Granular syenitic rocks repeated twice, perhaps even three times, in primitive intermediary (and secondary) deposits, are analogous phenomena with which we have become acquainted within these fifteen years. This disagreement in regard to age of great homonymous formations, does not by any means seem to me to be proved as yet by direct observations, made upon the contact of superimposed formations. The chalk or Jura limestone may, on one hand, immediately cover primitive granite, and, on the other, be separated from it by numerous secondary and transition rocks: these very common facts demonstrate only the abstraction, the absence, or non-development of several intermediary members of the geognostical series. The greywacke may, on one hand, dip beneath a felspar rock, or rock of which felspar forms a principal constituent; for example, beneath transition granite or zircon syenite; and, on the other hand, be superimposed upon the black limestone containing madrepores; but this position shows only the intercolation of a bed of greywacke between felspar rocks. Since the minute investigation of fossil organic bodies has, through the important labours of Messrs Cuvier and Brongniart, diffused a new life as it were in the study of the tertiary formations, the discovery of the same fossils in analogous beds of very distant countries, has rendered the isochronism of very generally extended formations still more probable.

It is this isochronism alone, this admirable order of succession, which seems given to man to investigate with some degree of certainty. The attempts which theological geologists have made to subject the periods to absolute measurements of time, and to connect the chronology of ancient cosmogonic narrations with the observations of nature, could not possibly have been productive of satisfactory results. "It has been more than once," says M. Ramond, in a discourse replete with philosophical views, "thought that a supplement to our short annals might be found in the monuments of Nature. There is, however, enough of historical ages, to let us see that the succession of physical and moral events, is not regulated by the uniform progress of time, and could not consequently give it measure. We see behind us a series of creations and destructions, by means of the strata of which the crust of the earth is composed. They give rise to the idea of so many

distinct periods; but these periods, so fertile in events, may have been very short, in comparison with the number and importance of the results. Between the creations and destructions, on the other hand, we see nothing, however vast the intervals may be. There, where all is lost in the void of undetermined antiquity, the degrees of relative age have no appreciable value; because the succession of phenomena has no longer the scale which relates to the division of time." (Memoires de l'Institut, for the year 1815, p. 47.)

In the geognostical monography of a deposit of small extent, for example, the environs of a city, one cannot distinguish with sufficient minuteness the different beds which compose the local formations, shelving banks of sand and clay, the subdivisions of gypsums, the strata of marly and oölitic limestone, designated in England by the names of Purbeck Beds, Portland Stone, Coral Rag, Kelloway Rock, and Corn Brash, then acquire a great degree of importance. Thin beds of secondary and tertiary formations, containing assemblages of very characteristic fossil bodies, have furnished, as it were, a horizon to the geognost. In their prolongation, whatever occurs placed above or beneath in the order of the whole series, has been referred to one of them. Even the particular denominations by which beds are distinguished, are of much importance in a geognostical description, however whimsical or improper may be their signification or their origin as taken from the fanguage of miners. But while treating of the relative position of rocks on a surface of great extent, it is indispensably necessary to consider the formations, or habitual associations of certain beds, in a more general point of view. It is then that discretion and circumspection are more necessary in the distinction of rocks, and in their nomenclature. The work of M. Freiesleben on the Plains of Saxony, which are upwards of seven hundred square leagues in extent (Geogr. Beschr. des Kupferschiefergebirges, 1807-15), presents a beautiful model of the union of local observations and geognostical generalizations. These generalizations, these attempts to simplify the system of formations, and to direct the attention more especially to great characteristic features, should be more or less cautiously conducted, according as one describes the basin of a river, an isolated province, a great country such as France or Germany, or an entire continent.

The more minute the investigation of districts becomes, the more does the connexion between formations which appear at first perfectly independent, manifest itself by the great phenomenon of alternation; that is to say, by a periodical succes

sion of beds which present a certain analogy in their composition, and sometimes even in certain fossil organic bodies. It is thus that, in the transition-mountains, for example, in America (at the entrance of the plains of Calabozo), beds of greenstone and euphotide, in Saxony (near Friedrichswalde and Meissen) the clay-slates with glance-coal, the greywackes, porphyries, black limestones, and greenstones, constitute, from their frequent and repeated alternation, a single formation. It often happens that subordinate beds appear only at the extreme limits of a formation, and assume the aspect of an independent formation. The cupreous and bituminous marls (Kupferschiefer), which occur in Thuringia between the alpine limestone (zechstein) and the red sandstone (rothes liegende), and which have for ages been extensively wrought, are represented in several parts of Mexico, of New Andalusia, and of Southern Bavaria, by multiplied beds of marly clay, more or less carburetted, and included within the alpine limestone. Similar circumstances often give to gypsums, sandstones, and small beds of compact limestones, the appearance of particular formations. Their dependence on subordination is known by their frequent association with other rocks, by their want of extent and of thickness, or by their total suppression, which is frequently observed. It must not be forgot (and this fact has struck me much in the two hemispheres) that the great formations of limestones, for example, the alpine limestone, have their sandstones, as the very generally extended sandstones have their limestone beds. Thin beds of sandstones, of limestones, and of gypsums, characterize, in all the zones, the deposites of coal and rock-salt or muriatiferous clay (salzthon), isolated deposites, which are most commonly only covered by these small local formations. It is by overlooking these considerations, which should be familiar to every practical geologist, that the type of the great independent formations has been rendered too complicated.

The phenomenon of alternation manifests itself, either locally in rocks, superimposed several times upon each other, and constituting a single compound formation, or in the series of formations considered in their aggregate. It is either greenstones and syenites, slates and transition limestones, beds of limestones and of marl, that alternate immediately, or the whole is a system of mica-slates, and of granular feldspathic rocks (granites, gneisses, and syenites), which reappear among the transition deposites, and which separate from the primitive homonymous system the greywackes and limestones with orthoceratites. For the first knowledge of this fact, one of the most important and least studied of modern geognosy, we are