Page:The Annual Register 1899.djvu/520

 96 SCIENCE. [1899.

Her Majesty's ship Penguin, on a surveying cruise in the Pacific, has taken soundings between Auckland and the Tongan Archipelago to a depth of 28,572 feet. Falcon Island, that was formed during a volcanic eruption in 1885, and vanished in 1898, was detected eighteen feet below the surface of the sea.

Little success has attended the effort to ascertain the course of oceanic streams by means of floats. They are too easily driven by the wind, and they cannot follow the water when it descends to form an undercurrent.

Admiral Makaroff maintains that double currents in marine straits depend on differential salinity. The specific gravity due to salt is, in the water of the Black Sea, only half of that which obtains in the Medi- terranean, and the considerable difference in density so caused produces an inrush by a bottom current which raises the level of the Black Sea, and a superficial current is compelled to flow in the opposite direction. Similarly, the evaporation of water from the Mediterranean being greater than the quantity supplied by rivers and rains, that sea becomes dense and forces its way into the Atlantic by an undercurrent.

On the other side, Admiral Wharton considers that differential tem- perature, and especially the prevalent direction of wind, are the prime factors. The surface water, of low density, in the Dardanelles, is at times stagnant, and at times it flows towards the Black Sea. In the Strait of Bab-el- Mandeb, where there is a surface inflow, and an outflow at the depth of 100 fathoms, the specific gravity of the two currents is respectively 1*0279 and 1-0292 ; and this difference is insufficient to set up streams flowing in opposite directions at the rate of one and a half knots an hour.

Geology.

Glaciated pebbles have been found in coal seams at the base of the permocarboniferous system in New South Wales. They are thought to have been transported by floating ice. Evidence of glacial action in Upper Palaeozoic times has been met with in India, South Africa, Australia and South America.

On the other hand, Professor Watts has described a smoothed and grooved surface of Mount Sorrel granite underlying undisturbed Keuper marl ; and it was held that these markings were produced by wind- driven sand, and were evidence of desert condition in Triassic times.

The Rev. Osmond Fisher has examined the residual effects of a land glaciation on underground temperature with the view to an estimation of the lapse of time since the disappearance of ice. When the method suggested, which is a comparative plotting of temperature gradients, is applied to the well at Wheeling, in the United States, 4,99Q feet deep, an effect is brought out opposite to that anticipated ; and when it is applied to a deep mine in the neighbourhood of Lake Superior, the result is obtained of an original surface temperature of - 66° Fahr., which is in- credibly low, since it is known that land covered with ice does not fall much below 32° Fahr. His conclusion is that a date for the glacial epoch cannot be obtained from a study of underground temperatures.

The same inquirer has examined Lord Kelvin's estimate of geolog-