444 Probable influence of 



detritus, borne down by rivers or moved by currents, are 

 deposited, as the instances of this aground at the mouth of 

 the La Plata or the Banks of Newfoundland, would be, in 

 time, surrounded by the loose materials ; the dissolution or 

 foundering of the berg would present hollows like those seen 

 in the drift ; or the iceberg might protect the bank upon 

 which it was aground, and prevent it from being washed 

 away, while the materials all around might be carried away. 

 The dissolution of the berg would leave a hill. 



In connection with the subject of drift, it is interesting to 

 observe the direction in which the present icebergs are carried 

 from their source, and the northern and southern limits of 

 their transport. Their general course, as is well known, is 

 from the polar towards the equatorial seas, transported as 

 they are by the currents which set from the poles towards 

 the equator. If the northerly and southerly direction of these 

 polar currents is due to the excess of evaporation in the 

 warmer seas, and a flow of water from the colder oceans to 

 supply the loss, a theory which has been proposed by the 

 French philosophers, although I hardly dare to suggest any 

 theory, similar currents must have prevailed in the ancient 

 frozen seas, so that the ancient currents must have corres- 

 ponded with the general course of the drift. 



The facts collected, as to the northern and southern limits 

 of the transport of ice, are as follows: Captain Crocker, of 

 New Bedford, who has crossed the ocean in command of a 

 packet ship one hundred and sixty-four times, says that he 

 never saw icebergs south of the 40th degree of latitude, and his 

 impression is that all seen south of the 46th degree are small. 

 Captain Luce, of New Bedford, has seen them in 41° north 

 latitude. Thev have been seen near the Azores, in latitude 

 4*2°. Captain Lane, of Portsmouth, informed me that, in 

 the year in which the President was lost, in going to Mar- 

 seilles, his ship came near striking an iceberg in about 41°, 

 and as fiir east as the 19th degree of longitude. There is no 

 evidence of their having been seen in the northern hemisphere, 

 south of latitude 40^. In southern latitudes, icebergs have 



