B. Chambers on Ancient Sea Margins. 33 



diminution occurs as the latitude is increased." The mean eleva- 

 tion of the barometer in the Antarctic latitudes is about an inch 

 greater than in other parts of the world. " It had been considered 

 that the mean pressure of the atmosphere at the sea level was 

 nearly the same in all parts of the world, as no material difference 

 exists between the equator and the highest parts of the world."' 

 Sept. 2. — They descried the shores of Old England ; the ships 

 anchored off Folkstone, and in the morning the commander of 

 the expedition hastened to London to make his report to the Ad- 

 miralty.— B. S., Sn. 



Art. III. — On Ancient Sea Margins ; by R. Chambers, Esq., 

 (from a letter to one of the Editors, dated Edinburgh, April 

 10, 1849.) 



* 



I have read with much interest, Mr. Dana's remarks on my 

 ' Ancient Sea Margins,' inserted in your Journal for January, and 

 reprinted in this month's number of Jameson's Edinburgh New 

 Philosophical Journal. These remarks do not the less please 

 me, that they are mainly an expression of the doubts and diffi- 

 culties which the announcement of the subject is apt to raise in 

 an ingenious and enlightened mind. I should be most happy if 

 by a few observations in reply I could in any degree remove, or 

 even soften those doubts : for their complete removal I believe I 

 must be content to wait till one or two candid enquirers shall 

 take the trouble to go over the ground which I have traversed. 



Mr. Dana is perfectly right in his descriptions of river-side ter- 

 races, and in all his speculations as to their cause. They are un- 

 doubtedly the relics of sheets of alluvial matter which originally 

 filled the bottoms of the valleys where they occur. They mark 

 a former height at which the river had run, and the reason of 

 the river having cut down the original alluvial sheet so as to 

 leave only these terraces high above its present waters is un- 

 doubtedly the withdrawal of a body of water, which formerly 

 received the river, to a lower level. The matter is very much 

 overlooked in my volume, because few examples of such ter- 

 races had come under my attention in Scotland ; but it is amply 

 treated in a paper which I read in December last before the Royal 

 Society of Edinburgh, and which has been since printed in 

 Jameson's Journal. 



It is unfortunate that the 'Ancient Sea Margins' should have 

 contained so little on this subject, since, had the case been other- 

 wise, Mr. Dana's doubts might have been much extenuated, and 

 he might have left the American geologists in a more hopeful 

 frame of mind as to the line of investigation which I have hum- 



Secon-d Bmm, Vol. VHI, No. 22.— July, 1849. 5 



