Page:Popular Science Monthly Volume 26.djvu/149

Rh recognizing different marine deposits as of like age from their organic remains, terrestrial and fresh-water beds would in all probability be referred to widely differing epochs, and that some would be more probably classed with a past period than with others of the present time. The idea that marine and terrestrial faunas and floras were similar throughout the world's surface in past times is so ingrained in paleontological science that it will require many years yet for the fallacy of the assumption to be generally admitted. No circumstance has contributed more widely to the belief than the supposed universal diffusion of the carboniferous flora. The evidence that the plants which prevailed in the coal-measures of Europe were replaced by totally different forms in Australia, despite the closest similarity between the marine inhabitants of the two areas, should go far to dispose of this belief. Hence, determinations of the age of terrestrial beds based upon their fossil faunas and floras should not be accepted as fixed unless they are accompanied by evidence from marine beds.

Discussing the "Physiology of Deep-Sea Life" in the Biological Section, Professor Moseley, of the Challenger Expedition, having recognized the value of the work that had been done in deep-sea investigation in the United States, spoke of the importance to the physiologist of a knowledge of the conditions under which gases occur in a state of absorption in the ocean-waters. Professor Dittmar's researches show that the presence of free carbonic acid in ocean-waters is an exception. Hence, the solution which some shells undergo at certain depths is probably due, not to the presence of free acid, but to the solvent action of the seawater itself. Oxygen is present in all seawater, being derived from the surface, but the amount diminishes, on account of the oxidizing that is always going on, with increase of depth. M. Regnaud's experiments on the effects on organisms of high pressures, corresponding with those of certain sea depths, show that a fish without a swimming-bladder, or one with the bladder emptied of air, may be subjected to a pressure of 100 atmospheres, or 650 fathoms, without injurious effect; at 200 atmospheres, or 1,300 fathoms, it becomes torpid, but soon revives when the pressure is removed; while at 300 atmospheres, or about 2,000 fathoms, the fish dies. The results of these experiments would probably have been greatly modified, if plenty of time could have been given for the fish to accommodate itself to the change of pressures and the conditions in which it moves slowly from one depth to another be imitated. M. Paul Bert's experiments upon the effect on aquatic organisms of water subjected to the pressure of compressed air—a very different condition—show fatal results at fifteen and even at seven atmospheres. A large proportion of the food-supply of the deep-sea animals appears to be derived from life on the ocean-surface, or that which is brought to the surface by rivers from the land sinking down to it. Deep-sea life appears to diminish in abundance as the coasts are receded from. More may be known on this subject when we have learned more about pelagic vegetable life, with which our acquaintance is now imperfect. If it shall be ascertained that the deep sea derived its main supply from the coasts and land-surfaces in the early periods, there can have existed scarcely any deep-sea fauna until the littoral and terrestrial faunas and floras had become well established. It still appears impossible to determine any successive zones of depth in the deep-sea regions, characterized by the presence of special groups of animals. Some groups seem to be characteristic of water of considerable depth, but representatives of them struggle up into much shallower regions. This fact places a difficulty in the way of determining the depths at which the geological deposits were formed. Something may be learned of the depths of modern deposits by the examination of their microscopical composition and the condition of the shells and spicules. Great uncertainty prevails as to whether, or to what extent, the intermediate waters, which are held to include about eight ninths cf the bulk of the entire ocean, are inhabited by animals. A feature of the deep-sea fauna is the general absence from it—except as to mollusks and brachiopods—of palæozoic forms. This fauna has, doubtless, been derived almost entirely from the littoral fauna, which also must have preceded,