though they may have been due to birds. I may mention, that a friend in India (Mr. R. N. Mantell, since deceased) described to me in a letter, some large, broad, trifid markings that he saw on the sandbanks of the Ganges; they were of this shape (fig. 7), shallow, and with a well-defined edge. Tracing the track to where the sand was wet, he found them take the unmistakeable and unpretending shape of ordinary bird-tracks (fig. 8); "the sole and sufficient reason," said he, "of their gross exaggeration was the action of the wind on the fine dry sand." Trying prints of his own hand, he saw them slowly become augmented into broad caricatures of a hand-print by the same natural process.
Fig. 8.
On the figured slab of Wealden rock, from the Upper Hastings Series, near Cuckfield, Sussex (Pl. VII.), we have sun-cracks, raised gallery-markings, and many obscure trails, some corrugated, some smooth. It is possible that, as a friend has suggested to me, some of these may be the marks of roots of aquatic plants; but there is no direct evidence on the subject. Root-like markings, however, small, vertical, and numerous, occur abundantly in the Hastings sand-rock, as pointed out to me by my friend Mr. J. Morris (see fig. 9).
During the autumn of the same year as that in which I collected the recent trail-marked mud in the Isle of Wight, I was in the Weald of Kent, and, examining a brick-field, I saw a pond lessened by drought, and on its mud were prints of a dog's feet, small hollow trails, and convex galleries, such as those before noticed (fig. 10). The roofs of some of these last were so thin they were split, and in some cases removed. Besides the markings above mentioned, the drying clay had another interesting feature, namely, a partial coating of minute globular bodies (fig. 10 a), mostly lying closely packed in single layer, but sometimes crowded irregularly, and occasionally scattered about loosely. These are of the same colour as the clay, and are probably the ova of the Boat-fly (Notonecta) , thinly coated with clay; and their interest lies in the fact that in Mexico allied insects are known to lay a profusion of large ova in the Lake of Tezcuco, and that there they become petrified into an oolite. The fact has been described by M. Virlet d'Aoust, in the 'Bulletin de la Soc. Géol. de France,' 2e Sér., vol. xv. p. 200, etc., 1858, who, noticing the oolitic structure of the recent limestone on the margin of the salt-water lake of Tezcuco, near Mexico,[1] learnt from Mr. J. C. Bowring, the manager of the salt-works there, that the oolitic granules were nothing more than the eggs of certain insects, encrusted and cemented together by the calcareous sediment of the lake. The eggs, too, being attached by little stalks or pedicels, are the more readily coated with the lime all over, and keep their relative position the more firmly.
- ↑ See the memoir for some interesting information on the relationships of the great freshwater and salt lakes of the Mexican plateau; also, E. B. Tylor's 'Anahuac,' 1859.
