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Show 588 ASCE~SION. July, 1836·~ as a building stone ; but some of the layers are too hard for freestone, and when struck by the hammer ring like flint. The main line of beach is directed N.E. and S.W. ; Lieutenant Evans informs me, that during the six months included between the 1st of April and the 1st of October, the sand accumulates towards the N.E. extremity, and during the other six it travels back again towards the S.W. end. This periodical movement is due to a change in the direction of the swell, which is influenced by the general direction of the trade-wind, during the two periods of the year. Lieutenant Evans also informs me that during the six years he has resided on this island, he has always observed, that in the months of October and November, when the sand commences travelling towards the S.W., the rocks which are situated at that end of the long beach, become coated by a white, thick, and very hard calcareous layer. I saw portions of this remarkable deposit, which had been protected by an accumulation of sand. In the year 1831 it was much thicker than during any other period. It would appear that the water, charged with calcareous matter by the disturbance of a vast mass of calcareous particles, only partially cemented together, deposits this substance on the first rocks against which it impinges. But the most singular circumstance is, that in the course of a couple of months this layer is either abraded or redissolved, so that after that period, it entirely disappears. It is curious thus to trace the origin of a periodical incrustation on certain isolated rocks, to the motion of the earth with relation to the sun ; for this determines the atmospheric currents, which give the direction to the swell of the ocean, and this acts on the arrangement of the sea-beach, and this again on the quantity of calcareous matter held in solution by the waters of the neighbouring sea. One of my excursions took me towards the S.W. extremity of the island. The day was clear and hot, and I saw the island, not smiling with beauty, but staring with naked Aug. 1836. BAHIA-BRAZIL. 589 hideousness. The lava streams are covered with hummocks, and are rugged to a degree, which, geologically speaking, is not of easy explanation. The intervening spaces are concealed with layers of pumice, ashes, and volcanic tuft. In some parts rounded volcanic bombs, which must have .assumed this form, when projected red-hot from the crater, lie strewed on the surface. Whilst passing at sea this end of the island, I could not imagine what was the nature of the white patches, with which the whole plain was mottled; I now found they were seafowl, which were sleeping in such full confidence, that even in midday a man could walk up to, and seize hold of them. These birds were the only living creatures I saw during the day. On the beach a great surf, although the breeze was light, was tumbling over the broken lava rocks. Upon leaving Ascension the ship's head was directed towards the coast of South America, and on August 1st, we anchored at Bahia or San Salvador. We staid here four days, in which time I took several long walks. I was glad to find my enjoyment of tropical scenery had not decreased even in the slightest degree, from the want of novelty. The elements of the scenery are so simple, that they are worth mentioning, as a proof on what trifling circumstances exquisite natural beauty depends. The country may be described as a level plain of about three hundred feet in elevation, which in every part has been worn into flat-bottomed valleys. This structure is remarkable in a granitic land, but is nearly universal in all those softer formations, of which plains usually are composed. The whole surface is covered by va~ous kinds of stately trees, interspersed with patches of cultr~ated ground, out of which houses, convents, and chapels arise. It must be remembered that within the tropics, the wild luxuriance of nature is not lost even in the vicinity of large cities ; for the natural vegetation of the hedges and hill-sides, overpowers in picturesque effect the artificial labour of man. Hence, there |