28'^ American Association. 



remarkable facts by elevating tbe pole of tbe terrestrial globe 

 twenty-one and a-balf degrees above the horizon and then caus- 

 ing the globe to revolve. The northern line of South America, 

 a portion of the coast of Africa, a portion of the Central American 

 coast, most of the Pacific Islands, &c. were portions of great circles, 

 tangent to the tropics. Prof. Pierce said this seemed to indicate 

 that the sun had someting to do with the formation of continents; 

 Indeed the sun had very great influence even now, and when, at the 

 formation of the earth the mass was in a fluid state, the difference 

 of one or two degreess might make all the difference whether 

 congelation should take place at one time during the day or not. 

 And the action of the sun, in allowing the mass to cool or grow 

 warm, to congeal or solidify, would cause a tendency to the for- 

 mation of lines of cleavage in the mass or crust of the earth. 

 These lines of cleavage were all that geologists required to enable 

 them to account for the formation of chains of mountains and 

 lines of coasts. The solidifying of certain portions of certain 

 continents would account for the formation of ocean currents. 



PHYSICAL GEOGRAPHY OF AFRICA. 



Professor Guyot read an interesting paper on the little known 

 and hitherto apparently exceptional physical geography of Africa, 

 basing his conclusions on the discoveries of Barth, Livingstone, 

 and other late travellers. "We are sorry that we cannot give an 

 abstract of this paper, 



DIRECTION OF THS CURRENTS OF DEPOSITION AND SOURCE OF 

 THE MATERIALS OF THE OLDER PALEOZOIC ROCKS. 



Glimpses of large views on this subject have been given at 

 various times by Prof. Hall and his brother Geologists of the 

 United States. Li the present paper Prof. Hall gave a large 

 extension to our previous conceptions of the subject, assigning in 

 the formation of mountains an influence to sedimentary deposition 

 which geologists have not hitherto attributed to it. Prof. Hall's 

 view on this subject, may be overstrained, but it embraces im- 

 portant general truths, not to be neglected in any attempt to 

 explain in detail the formation of our continents. 



" He said that in treating of the elevation of mountains, suffi- 

 cient consideration had not been given to the distribution of the 

 material forming these mountain chains, in its unaltered condition. 

 All the materials they knew of were stratified, and had been 



