MARKINGS, FOOTPRINTS AND FUCOIDS 313 



transient, these pits retain their shape permanently, being dried 

 by the sun, and being then too firm to be effaced by the 

 action of the succeeding tide, which deposits upon them a new 

 layer of mud. Hence we find, on splitting open a slab an 

 inch or more thick, on the upper surface of which the marks 

 of recent rain occur, that an inferior layer, deposited perhaps 

 ten or fourteen tides previously, exhibits on its under surface 

 perfect casts of rain prints which stand out in relief, the moulds 

 of the same being seen in the layer below." 



After mentioning that a continued shower of rain obliterates 

 the more regular impressions, and produces merely a blistered 

 or uneven surface, and describing minutely the characteristics 

 of true rain marks in their most perfect state, Sir Charles 

 adds : — 



" On some of the specimens the winding tubular tracks of 

 worms are seen, which have been bored just beneath the 

 surface. Sometimes the worms have dived beneath the sur- 

 face, and then re-appeared. Occasionally the same mud is 

 traversed by the footprints of birds {Tringa minutd)^ and of 

 musk-rats, minks, dogs, sheep and cats. The leaves also of 

 the elm, maple and oak trees have been scattered by the 

 winds over the soft mud, and having been buried under the 

 deposits of succeeding tides, are found on dividing the layers. 

 When the leaves themselves are removed, very faithful im- 

 pressions, not only of their outline, but of their minutest veins, 

 are left imprinted on the clay." 



This is a minor illustration of that application of recent 

 causes to explain ancient effects of which the great English 

 geologist was the apostle and advocate, and which he so 

 admirably practised in his own work. It is also an illustration 

 of the fact that things the most perishable and evanescent 

 may, when buried in the crust of the earth, become its most 

 durable monuments. Footprints in the sand of the tidal shore 

 are in the ordinary course of events certain to be obliterated 



