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Show 625 ADDENDA. say, "The ice lay much closer here; and numerous masses adhered to the bottom, under the water, which obliged us to search a passage out from the shore." Further on (p. 220) they say, '' But nowhere had the thaw penetrated more than two inches beneath the surface (of the land), while under water along the shore, the bottom was still impenetrablg frozen." This was on the second of August. It should, however, be observed, that the sea alo_!lg this part of the American coast is extremely shallow. Page 321. I have given my reasons for believing that the temperature of the mineral springs of Cauquenes, was permanently changed by the earthquake of 1822. This inference is altogether false, for I find that Schmidtmeyer, in his Travels in Chile during the years 1820 and 1821, says (p. 31 I) that the temperature of the different springs was 83°, 103°, 106°, ll2°, 117° and ll8° of Fahrenheit. Now Mr. Caldcleugh says, after the earthquake of February, 1835, the temperature fell from 11so to 92°. Previously, therefore, to this shock, it had regained the tempera-ture which it had in 1820. · Page 377. When I offered my views on the cause of the great waves, which follow eartl~quakes on cer~ain coasts, I was not aware of the paper on this subject by S1r James Hall m the Edinhm'gh Royal Transactions, vol. vii., p. 154. I cannot, however, perceive the necessity of a sudden elevation of the hotto~, to produce tl~e observed effects, as supposed by that distinguished philosopher. Havmg read the abstract of a Notice on the Resistance of Water, by Mr. Russell, I perceive the subject is far more intricate, than I was at the time aware. Page 381. I have said that during the few months subsequently to the great shock of February, 1835, at Concepcion, upwards of three hundred tremours were felt, b.ut I should have said, within twelve days. (See Geograpll. Journal, vol. VI.,~· 3~2. Sketch of Surveying Voyage of the Adventure and Beagle, by Captaan FttzRoy). From some additional information which I have met with since finishing this chapter, I find the train of volcanic phenomen~ wl\ich followed this earthquakt>, affected a larger area than that mentiOned (seven hundred by four hundred miles), and affected it in a mann~r ~h~ch gives great additional weight to the argument that South Amenca Ism that part a mere crust resting over a sheet of fluid rock; ADDENDA. 627 and likewise to the generalization that the action of volcanoes, and the permanent elevation of the land (and consequently, as I believe, the elevation of mountain chains) are parts of the same phenomenon, and due to the same cause. Page 446. When I put together the few and exceedingly imperfect remarks on the subject of Miasmata, I did not know of Dr. Ferguson's remarkable dissertation- the result of his investigations in Holland, Spain, Portugal, and the West Indies-on the Nature and History of Marsh Poison (Edinburgh Royal Transact., vol. ix., p. 273). He there clearly proves the fact, which had struck me with so much surprise, namely, that the driest districts, which, according to common notions, would be considered as the most healthy, are often singularly the contrary. In his concluding remarks, Dr. Ferguson says (p. 290), " One only condition, then, seems to be indispensable to the production of the marsh poison, on all surfaces capable of absorption, and that is the paucity of water, where it has previously or recently abounded. To this there is no 'exception in climates of high temperature; and from thence we may justly infer, that the poison is produced at a highly advanced stage of the d1ying process." And, from facts previously stated, it would appear that even in barren hilly countries, the banks of mountain torrents, which had been overflowed, sometimes became extremely insalubrious. In another place, Dr. Ferguson Slays, " It is from these (the dried and half-dried margins of lakes and marshes) that the poison uniformly emanates, and never from the body of the lake or pool; and I think it may be fairly presumed, that water, as long as it can preserve the figure of its particles above the surface, is innoxious, and that it must first be absorbed into the soil, and disappear from the eye, before it can produce any mischievous effects. Whoever in malarious countries waits for the evidence of putrefaction will, in all the most dangerous places, wait too long, as every one can testify who has seen pestilence teem forth, to the paralyzation of armies,-from the bare barren aands of the Alentejo in Portugal, the arid burnt plains of Estremadura in Spain, and the recently flooded table-lands of Barbadoes." I cannot forbear quoting here a remarkable fact, mentioned by Humboldt, though interpreted in a different manner by that illustrious traveller. Speaking of the intermittent fevers which are so common near the great cataracts, or rav.dales, of the Orinoko, he says (Pers. Nar., vol. v., p. 17) the causes '' are violent heats, joined with the excessive humidity of the air, bad nutriment, and, if we may believe the natives (as well as the missionaries), the pestilent exhalations that arise from the bare rocks o£ the raudales." Further on (p. 85), he says, "many examples are adduced of persons, who |