Page:Popular Science Monthly Volume 29.djvu/734

716 nodules and zeolitic crystals. It has not yet been possible to recognize the analogues of the deposits now forming in the abysmal regions in the rocks making up the continents, but it is quite otherwise in the areas bordering on the continents. Almost all the matter brought down to the ocean in suspension is deposited in this region, which is that of variety and change, with respect to light, temperature, motion, and biological conditions. It extends from the sea-shore down, it may be, to a depth of three or four miles, and outward horizontally from sixty to three hundred miles, and includes all partially inclosed seas. Plants and animals flourish luxuriantly near the shore, and animals extend in relatively great abundance down to the lower limits of the region. Here we find now in process of formation deposits which will form rocks similar to those making up the great bulk of continental land. Throughout all geological time the deposits formed in this border or transitional area appear to have been pushed, forced, and folded up into dry land, through the secular cooling of the earth and the necessity of the outer crust to accommodate itself to the shrinking solid nucleus within. The changes in the abysmal region, though great, are not comparable with these. The results of many lines of investigation seem to show that in the abysmal regions we have the most permanent areas of the earth's surface.

Rivers underground.—General R. Maclagan, describing the rivers of the Punjab before the Royal Geographical Society, remarks that, when the measure is taken of the water in a river flowing in a wide channel in soft soil, we do not at any time get the whole of it. We measure what is flowing above the bed, but there is more beneath. It sinks down till retained by some impervious stratum, and may become something like a second river flowing under the larger one which we see. It happens sometimes that the whole of a small stream sinks into porous soil and disappears, and, if a retentive stratum which it meets beneath comes out to the surface at a lower part of its course, the filtered water will pour out and become a surface river again, after the ordinary manner of streams. The experiment has been made on the Jumna of shutting off the whole visible river with a weir and turning it into the canals on either bank. A few miles below, the water trickles down into the bed again, and farther below there is a river as before. In most river-beds, like those of the Punjab, when they are left dry at the sides in the low season, water is to be got under the dry bed, as well as under the river, and usually at no great depth. Plenty of water can often be got by scooping a mere hole. The water-supply of Lahore is pumped from wells sunk in the bed of the Ravi. The water which sinks under the beds of these great rivers finds a wide field of hidden usefulness open to it when it gets beneath. Spreading abroad it meets, and helps to make, the great underground lakes and springs on which every country so largely depends. In the rainless tract around the meeting of the rivers in the south of the Punjab, this underground reserve of water is abundant and near the surface. In the distribution of the reserves there are great variations, according to the varying extent, form, and positions of the dividing walls of impermeable soil. The admission of water to new canals is commonly followed by the rise of the water level in wells within a certain distance on either side. Like the Mississippi, the Indus has in a part of its course raised its bed by the deposition of silt, so that for nearly four hundred miles it runs on an embankment made by itself, with long gentle slopes on both sides down to the general low level of the country. As along the Mississippi, the country is protected by dikes, and danger is apprehended in flood-times from crevasses.

Advantages of Sea-Voyages.—A medical writer in "Chambers's Journal" makes a warm recommendation of sea-voyages as a means of restoring health and strength. Among the chief advantages of a voyage are the perfect rest and quiet it secures. It is sure to take the passenger and keep him for a time out of the reach of all home annoyances and home drudgeries, and in many cases out of mind of them. He "has only to eat, sleep, and live. The strain of life is withdrawn. The wheels of existence move easily and with lessened friction. The incessant emulation, the keen anxieties, the