rarely be traced many yards without varying in size, and often coming to an end abruptly. (See Fig. 2.) There is also another phenomenon of frequent occurrence. We find a series of larger strata, each of which is composed of a number of minor layers placed obliquely to the general planes of stratification. To this diagonal arrangement the name of "false stratification" has been given. Thus in the annexed section (Fig. 3.) we see seven or eight Fig. 3. b Section of sand at Sandy Hill, near Biggleswade, Bedfordshire. large beds of loose sand, yellow and brown, and the lines a, b, c, mark some of the principal planes of stratification, which are nearly horizontal. But the greater part of the subordinate laminæ do not conform to these planes, but have often a steep slope, the inclination being sometimes towards opposite points of the compass. When the sand is loose and incoherent, as in the case here represented, the deviation from parallelism of the slanting laminæ cannot possibly be accounted for by any rearrangement of the particles acquired during the consolidation of the rock. In what manner then can such irregularities be due to original deposition? We must suppose that at the bottom of the sea, as well as in the beds of rivers, the motions of waves, currents, and eddies often cause mud, sand, and gravel to be thrown down in heaps on particular spots, instead of being spread out uniformly over a wide area. Sometimes, when banks are thus formed, currents may cut passages through them, just as a river forms its bed. Suppose the bank A (Fig. 4.) to be thus formed with a steep sloping side, and the water being B C in a tranquil state, the layer of sediment No. 1. is thrown down upon it, conforming nearly to its surface. Afterwards the other layers, 2, 3, 4, may be deposited in succession, so that the bank BCD is formed. If the current then increases in velocity, it may cut away the upper portion of this mass down to the dotted line e (Fig. 4.), and deposit the materials thus removed farther on, so as to form the layers 5, 6, 7, 8. We have now the bank B C D E (Fig. 5.), of which the surface is Fig.5. 10 9 B almost level, and on which the nearly horizontal layers 9, 10, 11, may then accumulate. The opposite slope of the diagonal layers of successive strata, in the section Fig. 3., may be accounted for by changes in the direction of the tides and currents in the same place. The ripple mark, so common on the surface of sandstones of all ages (see Fig. 6.), and which is so often seen on the sea-shore at low tide, seems to originate in the drifting of materials along the bottom of the water, in a manner very similar to that which may explain the inclined layers above described. This ripple is not entirely confined to the beach between high and low water mark, but is also produced on sands which are constantly covered by water. Similar undulating ridges and furrows may also be sometimes seen on the surface of drift snow and blown sand. The following is the manner in : which I once observed the motion of the air to Fig. 6. www Slab of ripple-marked (new red) sandstone from Cheshire. produce this effect on a large extent of level beach, exposed at low tide near Calais. Clouds of fine white sand were blown from the neighbouring dunes, so as to cover the shore, and whiten a dark level surface of sandy mud, and this fresh covering of sand was beautifully rippled. On levelling all the small ridges and furrows of this ripple over an area several yards square, I saw them perfectly restored in about ten minutes, the general direction of the ridges being always at right angles to that of the wind. The restoration began by the appearance here and there of small detached heaps of sand, which soon lengthened and joined together, so as to form long sinuous ridges with intervening furrows. Each ridge had one side slightly inclined, Fig. 7. b and the other steep; the lee side being always steep, as b, c,—d, e; the windward side a gentle slope, as a, b,—c, d, Fig. 7. When a gust of wind blew with sufficient force to drive along a cloud of sand, all the ridges were seen to be in motion at once, each encroaching on the furrow before it, and, in the course of a few minutes, filling the place which the furrows had occupied. The mode of advance was by the continual drifting of grains of sand up the slopes a b and c d, many of which grains, when they arrived at b and d, fell over the scarps b c and d e, and were under shelter from the wind; so that they remained stationary, resting, according to their shape and momentum, on different parts of the descent, and a few only rolling to the bottom. In this manner each ridge was distinctly seen to move slowly on as often as the force of the wind augmented. Occasionally part of a ridge, advancing more rapidly than the rest, overtook the ridge immediately before it, and became confounded with it, thus causing those bifurcations and branches which are so common, |