VI. OP THE FLOOD TIDE. H 



the world's history which was most fruitful in producing the present form, and filling 

 up, of our globe, the most active, so to speak, in preparing it for its most perfect 

 development of life ; and will apply to it some of the views which readily suggest 

 themselves. 



It may be premised, however, that the same views might also be applied to 

 earlier periods of geology. During the first period of organic life, the indications 

 are, I beUeve, that there were numerous and widely extended seas of Uttle depth, 

 and long shallow beaches, over which the wave of translation would have had free 

 play. But whatever may have been the temporary prevalence of the laws of 

 aqueous deposit during any particular period, as the old red sandstone, or the 

 cretaceous, it is certain that the present form of the earth's crust is due to other 

 causes, to mighty revolutions "which elevated entire mountain districts and 

 depressed others." (Agassiz, Edin. New Phil. Jaurn., No. 35, 1843, p. 4.) A period 

 which produced faults, dislocations, and protrusions, that remain the lasting evi- 

 dences of the violence that reigned at that epoch. 



But the period to which the views that have occurred to me seem particularly to 

 apply, is that subsequent to the tertiary, and preceding the drift, which is supposed 

 to have supphed, or must have supplied the drift material, and over which, on 

 several accounts, the tides and currents of the ocean must have exercised a great 

 and permanent influence. A greater influence than now ; because, the matter sub- 

 jected to their action was much more abundant, and the field over which it was 

 exerted was much more extensive, owing to the greater portions of the European 

 and American continents being under the sea. The epoch of the retreat of the 

 glacial period, as it is called by Agassiz, is the one referred to. The movement of 

 the masses of loaded ice, and the numerous floods formed from the melting ice and 

 snow, both carried with them that immense quantity of diluvium and sand, the 

 detritus of older periods, either made by the ice, and the atmospheric changes 

 accompanying it, or collected by the flood from older degradations, which form the 

 superficial covering of the earth over all its vast plains and slopes. A large portion 

 of this material was carried to the sea; a portion of it was dropped in the progress 

 thither. That which has come in contact with the water, and has been subject to 

 its action, is distinguished by stratification. It is worthy of remark here, that these 

 two characters of the materials, the stratified and unstratified, are found in close 

 connection with each other, owing to the different changes in the level of the sea. 

 Mr. Agassiz has pointed out an interesting example of this in Cambridge, Massa- 

 chusetts, near Mount Auburn, in the valley of the Charles River, where there is a 

 superficial deposit of stratified sand, overlying the unstratified drift. Every exca- 

 vation in similarly constituted regions, and the constant recurrence of the valley 

 formations, particularly on the eastern slope of this continent, taken in connection 

 with the materials with which these valleys are filled up, abundantly show that the 

 surface deposit has been carried down to the sea in and by aqueous forces operating 

 on the surface of the elevated lands. At the period referred to, these forces were 

 most active ; the streams, as appears from the examination of their ancient beds, 

 were great and impetuous; the amornit of material transported was immense. If, 

 when this material was brought down to the sea border, and subjected to the power 



