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has its rise, and course, entirely in a granite country before it passes through the great black soil or regur plains of Bellary-whose granite and gneiss are also the principal rocks.
The surface soil from Hydrabad southerly to the Kistnah near Myapore, is generally a reddish alluvium, sometimes more or less sandy, or clayey, according to the prevalence of felspar or quartz in the adjacent rock. It varies from the zero of the bare rock to 12 feet in thickness. Sometimes a bed of kunker, (from 6 inches to 2 feet thick) intervenes between it and the rock; but more frequently the loose gravelly debris of the subjacent granite or gneiss, which is extremely prone to decay on exposure to the air, or to moisture, whether from springs or rivers.
Where subterranean springs exist this bed of Mhurrum, as it is called, is sometimes from 30 to 50 feet thick; but, more commonly, water is found at depths from 6 to 30 ft. Springs impregnated with calcareous or saline matter seem to effect the breaking up of the rock to a greater extent than those of pure water.
Mr. Malcolmson,* in speaking of this granitic debritus, thus observes: "It has been stated by Dr Christie, that this debris is, at a considerable depth, again consolidated by pressure. In the Edinburgh Journal of Science, 1828-9, this is also mentioned as a fact, common to the rocks of other parts of India. With every respect for his authority, I cannot avoid the conviction, that the inference was founded on imperfect observation, and that it has since been employed in Europe, in support of an ill-founded theory. The Mhurrum' or gravel found in deepening a well at Bolarum (6 miles from Secunderabad) upwards of 50 feet deep, during the dry season of 1832, is not in the slightest degree consolidated." "Much of the debris of Secunderabad is, however, consolidated by lime, which is seen to agglutinate the fragments, or to pass in vein-like lines or nodules through the gravel. Occasionally there are only a few fragments of quartz or felspar scattered through the kunker, or they appear to be inserted into the surface." "The debris is also sometimes united into pulverulent masses, by the oxidation of the iron contained on the sienite; but this takes place at the surface, and seldom acquires any degree of hardness."
While perfectly coinciding with the general accuracy of my lamented
* Madras Journal, July 1836, p. 198.
friend's remarks, yet it cannot be denied that great and long continued pressure in general tends to consolidation. That it has not produced this effect on the gravel of some of the deeper wells at Hydrabad is, as Mr. Malcolmson observes, strictly the case, but consolidation has been counteracted in a great measure, by the continual state of moistness in which the debris is kept by the percolation of the spring water in its way upwards and the constant separation and shifting of the particles by water in motion. The temperature of a perennial spring of pure water in the garden of an Arab outside the city walls, I found to be 80° Faht. Temp. of air in shade-89°.
The temperature of the Bhugga, whence many of the Mahomedan nobles and the Minister Chundoo Lal procure water, was 79° 2′. Faht. Temperature of air in shade 87°.
The mean temperature of Hydrabad is I believe about 80°.-Height above sea by boiling point of water 1702 feet.
On my way to Hydrabad, at Mahanundipet, about 42 miles north of the Kistnah, date, June 4th, 1839, at 10° 15′ A. M., I witnessed a phenomenon rather rare in this part of India, viz.-an annular solar rainbow. Its radius, taken to the inner circle from the sun's centre, was 22° 30. It continued advancing with the sun towards the zenith, but disappeared gradually, before the meridian was attained, at an attitude of about 75°.
The sky was lightly veiled with thin grey clouds (cirri), amid which the sun shone with a watery light, and defined disc, encircled by four differently coloured, contiguous zones. The prismatic tint of the band nearest the sun was orange, then yellow, pale green, and violet in succession. The united breadth of the four zones amounted to 38'.
The wind was blowing strong and steadily from the west. The thermometer in shade 80°. It had been on previous days usually from 83° to 86° in the shade. At this time the temperature of the open air was 86°. All the lunar halos in this country which I have measured have a radius from 22' to 23°; and there is, in general, a slight depression in the thermometer at the time of their prevalence.
ON TEREDO NAVALIS and a natural defence against its ravages, by Mr. LEHMANN : from the Transactions of the Scandinavian Naturalists of Copenhagen, 1840; translated and communicated by Dr. T. CANTOR.
Teredo Navalis, an important agent in the economy of nature, is universally known by the damage it inflicts upon the wood work of posts and ships. While accomplishing the intention of nature in destroying decayed wood in the sea, it at the same time attacks ships, bulwarks and the piles of quays. Like all animals intended by nature to clear her stage, the Teredo is endowed with immense power of reproduction, and therefore by its numbers becomes more destructive than the largest animals which come in collision with the industry of man. Every museum exhibits specimens of wood perforated by this shell-fish, which lines its abode with lime, in composition similar to that of its shells. But my inquiries as to the length of time required by the animal to perforate the wood, have hitherto been fruitless. Some samples of the works of Teredines are here submitted, because I am enabled to attest the age of the artificers. Five years after the posts of bulwarks of Kyholm were erected they appeared in the state now exhibited. From these it will be seen that the Teredines, during the said period, have attained to their full size, of more than 12 inches in length, and half an inch in diameter. It may therefore be inferred, that they thrive, and combine quick growth with great multiplication.
The more important the works are, which are attacked by the Teredo, and the quicker the destruction is perpetrated, the greater the solicitude which has been exerted to defend the wood, and many applications have been tried, but none have stood proof in the sea. The only remedy hitherto successful, has been to cover the wood with plates of metal, of copper, brass or zinc. But they are too expensive to be used universally, nor are they easily protected.
herself, which I
The pilot and of the Eider,
I believe to have found a defence offered by nature therefore recommend to the attention of naturalists. light vessel, placed in the North-Sea, in the mouth requires not to be coppered, and, as she has to sail but few miles, is therefore provided with a sheathing of plain boards. The Teredo attacks the latter indeed, but cannot penetrate to the sides of the vessel,
as the interval between them and the sheathing is filled with a layer of cow-hairs. The boards of the sheathing are annually repaired or renewed. Last year it was reported that the sheathing required no renewal," although" it was thickly covered with muscles. This circumstance reminded me that I earlier had found no Teredines in bulwarks on which muscles (mytilus edulis), were fixed, an observation, which I however had not then followed up. At present I have reason to believe, that the sheathing of the pilot-vessel was not attacked, because it was covered by muscles. As the latter may easily be bred, they offer a natural defence, of no expense, and may besides be turned to economical account.
The muscle attaches itself to piles by means of the byssus, or filaments, and multiplies so readily that its young, if suffered, soon cover the whole surface. In the frith of Apenrade piles have, from time immemorial, been sunk, on purpose for the sake of the muscles, which in the course of four years attain to a length of 3 to 4 inches. They are consumed either in fresh state, or are pickled and exported in large quantities. The smaller muscles are thrown back near the piles to which they soon again attach themselves. The short period in which they will cover a surface, I have had an opportunity of observing, when a new light-vessel was placed near Laessöe in Kattegat. In 6 months her bottom was covered with a thick mass of young muscles, which had tended to impede the speed of the vessel. Two feet square of the mass, submitted to my examination, consisted of several layers of muscles, 2 inches in length, so firmly connected by the byssus, that a needle could not pass between them. No single muscle could be detached without the whole mass following.
Teredo breeds during the dog-days, the muscle some months earlier. Where the latter has fixed itself, the eggs of the Teredo cannot reach the wood, nay, by intercepting the communication with the sea, the muscle will suffocate Teredines, which may happen earlier to have found their way into the wood.
At first I supposed the byssus might possibly contain something specifically repulsive to the Teredo, and I therefore had it submitted to the chemical analysis of Dr. Scharling, which however has not given the result expected. It is the mere mechanical covering of the muscles, which prevents the Teredo from reaching the wood.
[The valuable hint contained in Dr. Cantor's communication will doubtless be appreciated by all such as are interested in the protection of wood-work from the attacks of the Teredo. Nowhere would this natural opponent of its ravages be more serviceable than in the Huglí; but the Mytilacea are, strictly speaking, inhabitants of salt water, although some of the family are capable of being localised in rivers, as is the case with Dreissina polymorphus, discovered by Pallas in the Volga, and some species of Modiola. The valves of two species of Mytilus have occasionally brought to me from the Hugli; one, closely allied to M. edulis, but less ventricose, and easily distinguished from it by the cardinal teeth; the other apparently identical with the M. crenatus of Lamarck, figured in the Conchologia Systematica of Reeves; but as neither of these, nor Dreissina, of which I have several specimens, have been found alive, I think their presence altogether accidental; they may have found their way to this river either with ballast or adhering to the bottoms of vessels. Modiola emarginata, (Benson,) however, inhabits the water of Tolly's nullah, as I was informed a few weeks ago by its distinguished describer himself. -J. W. L.]