88 AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE. 



all conditions of the atmosphere, but whether produced by electro-magnetic 

 influence or not he could not say, although he thought it not unphilosophic to look 

 iu that direction for their cause. 



DIRECTION OF THE CUERENTS OF DEPOSITION AND SOURCE OF THE MATERIALS OF THE 

 OLDER PALEOZOIC ROCKS. ET PROF. JAMES HALL. 



In treating of the elevation of mountains, the author remarked, sufficient 

 consideration had not been given to the distribution of the material forming 

 these mountain chains, in its unaltered eoadition. All the materials they knew of 

 were stratified, and had been metamorphosed more or less. He proposed to 

 occupy a few moments in following the direction of the ancient currents, and to 

 show their parallelism with the mountain chains in the Laurentiau Mountains, 

 north-east of them, which are nearly parallel to the Appalachian chain. The 

 Geological Survey would show whether these sediments were thicker to the 

 eastward' than to the westward; but he thought the direction of the currents 

 which deposited the materials forming the Appalachian chain, was from the north- 

 east. They had certainly good evidence, from the fact that the strata are of the 

 same age, and are much thicker from the north-easterly direction then from the 

 south-west. They gradually thin in that direction, and as he believed they were 

 deposited by water, the further from the source they would be the thinner. 

 They had reason to believe that in the south-west these strata were much thinner 

 than in the north. Taking the Hudson River group which consists of sediments 

 stretching to the south-west, with a thickness of 1000 feet to the north-east of us, 

 it thins down to 600 feet in Pennsylvania, and finally in the Mississippi valley tho 

 thickness is not more than 100 feet. Passing from the Hudson river group and 

 over a lapse of time, to the Oriskauy Sandstone we find the deposits from the 

 north-east. ' 



At Gasp6 the thickness is 7000 feet, in • New York 'it is reduced to a few 

 hundred feet, and the strata thin out in a westerly direction. The conclusion 

 he had arrived at was that along these lines of deposit where the greatest accumu- 

 lation of sediment has been made, is where we have the greatest elevation of 

 mountain chains. This merely coincides with the direction of the ancient cur- 

 rents, and the Appalachian mountain range has not been more uplifted than the 

 other portions of the country, or than the plain between these and the Atlantic. 

 In New York and Pennsylvania we get to the Potsdam Sandstone, and, therefore, 

 there was no uplifting of any previously exisring rocks before the Appalachian 

 chain. The folding and plication had commenced at an early period — at a period 

 before the upper Silurian Rocks were formed, and we find these strata plicated, 

 and uplifted and metamorphosed in a considerable degree. We get no lower 

 than the Potsdam Sandstone in any part of the Appalachian chain, and we can 

 demonstrate that no lower mass has had anything to do in giving us the elevation 

 of this mountain chain. The Professor then referred to his examination into other 

 formations in confirmation of his hypothesis that elevating forces had not caused the 

 uplifting of these mountain chains. On the contrary, if there had been no folding 

 and plication, this range of mountains, he thought, would have been twice as high 

 as they now are. 



