streams. into columns or prisms, in the way in which they are found in nature. Where, however, any combination of circumstances prevented this arrangement, the globular concretions would remain, an effect which Dr. Daubeny subsequently found a beautiful illustration of, in the volcanic region of Eifel, which is thus described: "A curious illustration of the formation of basalt occurs in a natural grotto, formed at the junction of two basaltic The walls of this grotto are composed of basalt, slightly cellular, and forming a number of concentric lamellar concretions, and somewhat compressed, so that the interstices between the balls are filled up. It obtains its name, cheese-cellar, from the similarity it presents to Dutch cheeses piled upon each other. It beautifully illustrates the origin of the jointed columnar structure, which this rock so often assumes, since a little more compression would have reduced these globular concretions into a prismatic form, each ball constituting a separate joint in the basaltic mass. The most probable way of accounting for the existence of this natural grotto, is, to suppose the lava which forms its walls to have cooled near the surface, before the mass had ceased to flow into its interior: hence, a hollow would be left in which the basalt had room freely to assume the form most natural to it, and the concretions, being but little compressed on account of the cavity within, retain their original globular figure. In further proof of this, it may be remarked, that the lava above the grotto consists of irregular prisms, and not of balls, as is the case with that which constitutes its walls." Some of the ancient basaltic columns of the Hebrides too, when stripped of their outer coats, appear to be composed of an accumulation of cannon-balls and bomb-shells, piled vertically upon each other. Thus does science become familiar with the arcana of nature, and in this manner sometimes anticipates her secret operations! CONCLUSIONS. To the hasty and imperfect outline of the leading facts and phenomena which geological research has brought to light, it remains now for us to glance at the hypotheses which they have suggested; to fill up the sketch, by introducing the causes which have produced the great physical changes, the effects of which we have faintly shadowed forth, and to throw over the whole a few reflections, which the contemplation of a subject so vast inspires. To the immediate agency by which many of the phenomena delineated have been produced, reference has been made in the body of the sketch: the causes which produced the extraordinary oscillations of land and sea, the dislocation and elevation of the strata, and the high temperature of the primeval earth-subjects which come within the range of physical astronomy, have engaged much of the attention of philosophers in recent times, and interesting and unlooked-for conclusions have resulted from the enquiry. All the facts we have considered conspire to prove that the earth, at early periods of its history, enjoyed a much higher temperature than at present; that the climate of the frigid zone, for instance, at the period of the formation of coal, was even hotter than that of the tropics in these days and there are many circumstances which : seem to indicate a gradual decrease of temperature, as a gradual approximation to the present state of things is observed. In the solution of this subject of enquiry all geological phenomena appear to be involved. A recent discovery in astronomy suggests a possible explanation of the cause of the decreased temperature.* It is evident that without the rays of the sun the surface of the earth would be densely cold: this is proved, if proof were wanting, by the cold which ensues from its temporary absence during the night, and the intense frost of the arctic regions during their long solar night. It is equally obvious that the mean temperature depends upon the mean quantity of the sun's rays received in a given period. Now it is ascertained that the elliptical orbit of the earth is undergoing a slow, but gradual approach to a circle, or in scientific language, the minor axis of the ellipse is gradually on the increase, while the major axis remains the same. The consequence, therefore, is clear, that the annual amount of solar radiation from this cause is gradually decreasing, as it must be inversely proportional to the minor axis of the ellipse, consequently the mean annual temperature is lowering. Hence we have a cause operating, as Sir John Herschel observes, in the right direction, but whether adequate or not, remains to be determined. Another astronomical cause has been suggested, and, in fact, was generally adopted by the early geologists, namely, a change in the position of the earth upon its axis, produced not gradually, as in the motion known to *See Herschel's Treatise on Astronomy; or Geological Transactions, 2nd series. astronomers in the precession of the equinoxes, but suddenly and violently by some external agency, such as that of the contact of a comet, which according to Whiston and others, was the secondary agency employed to produce the creation of the world and the deluge. But this change, whether brought about suddenly or by degrees, would have the effect only of bringing certain regions under the solar influence, which before had enjoyed but a scanty portion of the sun's rays; it might remove the polar regions to the equinoctial, and transfer the equator to the pole, but it is insufficient to account for that generally-diffused high temperature, which geological phenomena attest. Moreover, astronomers assure us that no permanent change in the position of the earth upon its axis can have been effected: there being in all rotating bodies not perfectly spherical an inclination to revolve on a certain axis in preference to all others, had any derangement occasioned by external violence taken place, equilibrium would have been speedily restored, and rotation upon its natural axis resumed. It is obvious, however, that the least oscillation or derangement in the motion of a ponderous body whirling with inconceivable velocity upon its axis, would produce an extraordinary effect upon its surface, more particulary upon the ocean, so sensitive that it invariably rises when in the presence of a planetary body, which never approaches within so short a distance as two hundred thousand miles. Some such violent catastrophe seems almost indispensable to effect the sudden revolutions of which we have geological evidence, such as those in which whole races of living beings were annihilated, solid strata turned upside down, or large |