Hypothetical High Tides

Abstract

I SHOULD like to be allowed to ask two questions on this subject: First. Could the vegetable accumulations from which the coal has resulted have escaped destruction if, during their subsidence, the world was subject to such tides as Mr. Ball postulates? It is difficult to understand how this could be if the shales and sandstones which overlie the coal be of marine or estuarine origin. Second. What do the Palæozoic conglomerates disclose on the subject? The shingle of beaches heaped up by the tide, having each layer of sand and pebble laid at the slope of the beach face, exhibits when cut at right angles to the trend of the beach the continuously oblique bedding which represents this slope, the vertical heights of the shingle bed thus laid up representing the extreme rise and fall of the tide and surges. This may be seen in the case of the Lower Eocene shingle in Bickley Cutting of the Dover Railway and in the case of the early Glacial shingle in deep pits at Henham and Halesworth in Suffolk. The latter show a tidal rise and fall there of more than twenty-five feet, the former not so much. The same structure obtains in the case of sandbanks left dry by the tide, and of such nearly all the Red Crag consists, the oblique layers of sand and shell corresponding to the oblique layers of sand and shingle in beaches. I have seen this structure extending for some distance in a railway cutting through Jurassic sandstone, but there was nothing to indicate that the tidal slope under which it was formed was greater than in the case of the Crag. It may be otherwise for aught I know with the old conglomerates, for I am not acquainted with them.