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Show 290 TIERRA DEL l?UEGO. June, 1834. very great weight in support of the mass of positive evidence which Mr. Lyell* has brought to bear upon the question. and the greater number of even the same coloured variety, as the grauitic rock, on which they rest, the case need not be considered. Secondly, in a late number of the Madras Journal, Dr. Benza has described some erratic blocks lying on a plain between the Neilgherries (lat. 12° N.) and Madras. He states that the foundation-rock of the country is gneiss, "while the granite clusters are more elevated, and affect either a prismatic form, or are piled up one on tlte otlter, like logging stones." Dr. Benza had the kindness to inform me that these masses are very large, and that several are piled one upon the other. Again, Brongniart says (Tableau de Terrains, p. 83), " On cite aussi dans l'Inde, au pays d'Hyderabad (lat. 17° N.), des blocs enormes de granite, amonceles les uns sur les autres" (Delnc neveu ). Every one must draw his own conclusions from these accounts, regarding the probability of erratic blocks being heaped up, one upon the other, like logging stones. The same doubt likewise partly applies to the Macao case. With respect to the boulders of Hyderabad, Dt·. T. Christie has distinctly stated (Edin. New Phil. Jour., Oct. 1828, p. 102), that they are in situ, and has explained their origin. For my own part, I cannot forget that whole granitic hills at the Cape of Good Hope, which, from weathering, have assumed a boulder-like form, were once described as transported masses. The two next cases do not properly come under consideration, for they refer to masses lying in the valleys of lofty mountains. We must not overlook such accidents as bursting of lakes, earthquakes, and the action of former coast-lines. Helms, in his Travels (English translation, p. 45), states he was astonished to find the highest snow-capped mountains near Potosi (20° N.) covered with a stratum of rounded granitic stones. He supposes they must have come from Tucnman, which is several hundred miles distant : yet at p. 55 he says, at Iocalla (a few leagues only from Potosi), "a mass of granite many miles in length, rises in huge weatherbeaten rocks :" the whole account is to me quite uninteiligible. Lastly, M. Gay ( Annales des Sciences, 1833) describes granitic boulders within the valley of Cauquenes (lat. 33°-34° S.), in the Cordillera. I ·visited this place: the boulders and pebbles are not large, and those beyond the mouth of the valley are small. The case did not appear to me nearly so extraordinary as it seems to have struck M. Gay. I cannot agree with his assertion that this rock is not found in that part of the Cordillera : but this is a subject which I shall discuss in a future work. i The absence of great embedded fragments in the formations of the secondary .epoch, when we know that the climate was of a more tropical character, is a fact of the same kind. June, 1834. RECAPITULATION. 291 The circumstance of a luxuriant vegetation with a tropical character so largely encroaching on the temperate zones, under the same kind of climate that allows of a limit of perpetual snow of little altitude, and consequent descent of the glaciers into the sea, is very important; because it has been argued, with great apparent truth, that as there is the strongest presumptive evidence of a gradual cooling down of the climate (or rather of a less favourable state for tropical productions) in Europe, it is most unphilosophical to imagine that formerly glaciers could have acted where they do not now occur. It may be asked; what are the circumstances in the southern hemisphere that produce such results ? Must we not attribute them to the large proportional area of water ; and do not plain geological inferences compel us to allow, that during the epoch anterior to the present, the northern hemisphere more closely approached to that condition, than it now does? We are all so much better acquainted with the position of places in our own, than in any other quarter of the globe, that I will recapitulate what is actually taking place in the southern hemisphere, t only transporting in imagination each part to a corresponding latitude in the north. On this supposition, in the southern provinces of France, magnificent forests, intwined by arborescent grasses, and the trees loaded with parasitical plants, would cover the face of the country. In the latitude of Mont Blanc, but on an island as far eastward as central Siberia, tree-ferns and parasitical orchidere would thrive amidst the thick woods. Even as far north as central Denmark, humming-birds might be seen fluttering about delicate flowers, and parrots feeding amidst the evergreen woods, with which the mountains would be clothed down to the water's edge. Nevertheless, the southern part of Scot- • Anniversary Address to the Geological Society, Feb. 19, 1836, p. 30; and Principles of Geology, vol. i., p. 269, and vol. iv., p. 47, fifth edition. t It is in the southern hemisphere that we find elephants, rhinoceroses, hippopotamuses, and lions, as far south as lat. 34° 35'. In South America the jaguat· occurs in 42°, and the puma in 53°. u 2 |