﻿156 GEOLOGICAL ACTION OF THE CURRENTS OF THE OCEAN. 



has been to increase the extent of land in the northern hemisphere, so an inquiry is 

 naturally suggested into the relation between this theory of the geological action of the 

 tides and that branch of physical geography which treats the progress of human 

 civilization and development as dependent upon the material form and structure of 

 those parts of the earth which have been successively inhabited by man. 



And, finally, when we consider that it is those deposits which have been subjected to 

 the influence and have followed the laws of tidal and current action that constitute 

 man's most convenient dwelling-place, that are best fitted to provide the means of his 

 support, and to facilitate intercommunication between the remote families of his race, we 

 are led to regard these regular and systematic movements of the ocean as the agencies 

 by which the earth was prepared for his reception, and as designed by Providence from 

 the beginning to be the instruments of those changes in the face of the globe which 

 were to precede the introduction of the human race, the great end of its creation. 



Note. — In the second section of this memoir, a particular description is given of the manner in which 

 indentations along the coast are converted into ponds by the gradual formation of alluvial belts across their 

 openings, the sand being deposited by the flood current. It is quite common to find in the drift of Cape Cod 

 several of these ponds lying along the same valley, or depression, one within the other, and separated by 

 bands, more or less broad, of sand and gravel finer than that of the hills. It may be supposed that, when the 

 communication between the innermost pond and the sea was open, the current, eddying round a projecting 

 point, continued at every successive tide to leave its burden, until finally an inclosure was formed by the junc- 

 tion of the belt to the opposite side of the bay. And so with the other ponds in succession. It has been 

 already remarked that these ponds are often deeper than the adjacent sea, and without doubt the tendency will 

 be to disunion at the shallowest parts. Profiting by what has been made known concerning the Aralo-Cas- 

 pian basin by Sir Roderick I. Murchison, in his Geology of Russia in Europe and the Ural Mountains, 

 an analogy of condition may perhaps be traced between the inland seas and lakes of Southern Russia and 

 the East, and the diminutive ponds of New England. This is truly parvis componere magna, but never- 

 theless the sentiment concerning time, which Sir Roderick has adopted as his motto, belongs equally to its cor- 

 relative space : — Le temps qui nous manque, ne manque point & la nature. 



" Judging," he says, " from the organic remains collected from numerous parts of the whole area, there 

 can be no sort of doubt that all the masses of water now separated from each other, from the Aral to the 

 Black Sea inclusive, were formerly united to this vast pre-historical Mediterranean." The Caspian evidently 

 was connected with the Black Sea through the Caucasian belt of sand, gravel, and shells, and the Aral and 

 Caspian interminged their waters through the low, sandy desert of Khivah. 



" The low level of the adjacent eastern districts would lead us to infer that it [this sea] spread over wide 

 tracts in Asia now inhabited by Turkomans and Kirghis," but it is not certain whether the lakes in this direc- 

 tion are also included in the same geological formation. It is interesting to know that the transition from 

 purely oceanic to brackish water deposits is indicated on the west (only) by a partial intermixture of shells of 

 each type (pp. 297 et seq.) The subsequent diminution of this vast body of water to such a capacity as 

 rendered possible the divisional deposits is a fruitful subject of speculation to the geologist, and is discussed 

 by Sir Roderick Murchison. 



