ILUVIATILE fORBitlONS. 203 



current is suspended by tlie rush of the tides, this mud is thrown 

 down, and very large, and widely extended tracts, of rich soil, 

 have thus been formed, and thousands of acres have been ex- 

 cluded from the encroachments of the sea by artificial embank-* 

 ments. At the time of very low tides, this soft mud is sometimes 

 exposed to the sun for several days, and thus becomes sufficiently 

 baked or consolidated, to a depth of several inches, to resist the 

 flow of water, which soon deposits upon it another thickness of 

 mud. We shall see that in a precisely similar manner, footprints, 

 of high antiquity, were formed in the strata of new red sand- 

 stone of the valley of the Connecticut, and also in Europe. 



The large rivers which flow from south to north in the northern 

 latitudes, having their sources in a much wanner latitude than 

 their mouths, become swollen in their progress northward, on 

 account of the ice which has not yet been broken up, hence they 

 overflow and sweep through the forests of pines and birches, and 

 carry away thousands of the uprooted trees- The timber thus 

 drifted down is often laden with the earthy deposit around the 

 roots, and beinjj deeply sunk in the water, other masses become 

 piled upon it until at length becoming water-logged it sinks and 

 is imbedded in the strata if there be any forming. "As the trees" 

 says Dr. Richardson, "retain their roots, which are often loaded 

 with earth and stones, they readily sink, especially when water 

 soaked ; and, accumulating in the eddies, form shoals which ul- 

 timately augment into islands. A thicket of small willows covers 

 the new formed island as soon as it appears above the water, and 

 their fibrous roots serve to bind the whole firmly together. Sec- 

 tions of these islands are annually made by the river, assisted by 

 frost, and it is interesting to study the diversity of appearances 

 they present, according to their different ages. The trunks of the 

 trees gradually decay until they are converted into a blackish 

 brown substance, resembling peat, but which still retains more or 

 less of the fibrous structure of the wood ; and layers of this often 

 alternate with layers of clay and sand, the whole being penetrated 

 to the depth of four or five yards or more, by the long fibrous roots 

 of the willows." A deposition of this kind, with the aid of a 

 little infiltration of bituminous matter, would produce an excellent 



