1865.] 



Notes and Correspondence. 



357 



On the Connection betiveen the supposed Inland Sea of the Sahara and the 

 Glacial Epoch. By Eev. Horatio J. Ward, M.A. 



A large number of our most emi- 

 nent geologists appear to have given 

 in their adhesion to the theory, that 

 the Glacial Epoch was coincident 

 with the period during which the 

 Sahara of North Africa formed the 

 bed of an ocean or vast inland sea. 

 Many, I believe, consider further, 

 that these physical conditions so 

 different to existing ones, were not 

 merely coincident, but were closely 

 connected as cause and effect, that 

 is to say, that the phenomena of 

 the Glacial Epoch may (to a certain 

 extent) be accounted for, by the 

 fact of the existence during that 

 epoch of an expanse of water, where 

 now is to be found only one of 

 sand. 



It would be needless for me to 

 dwell on the facts and reasons by 

 which this theory is supported, for 

 by this time they must be tolera- 

 bly familiar to most of the readers 

 of this periodical ; but so far as 

 I am acquainted with what has 

 been written on the subject, only 

 the immediate and direct influence 

 which the former of these two phy- 

 sical states exerted on the climate 

 and temperature of Southern, West- 

 ern, and Central Europe has been 

 touched upon ; whereas it appears 

 to me that the mdirect influences 

 must have been far greater and more 

 widely felt. 



It is upon these latter, then, that 

 I wish to broach a few ideas, trust- 

 ing that some of your wiser readers 

 will enlighten me if I am wrong, 

 or pursue the subject in your pages, 

 if so far I should be found right. 



My argument compels me to men- 

 tion first, some well-known and com- 

 mon-place facts. 



Everyone now-a-days is aware 

 that the warm climate of Western 

 and North-western Europe is owing 

 to the Gulf Stream ; but it is not 

 everyone who knows what are the 

 causes of this great current. Sub- 

 sidiary causes there may be, but 

 undoubtedly the main one is, the 



North-east trade-wind, blowing in- 

 cessantly, and with considerable 

 force, in the Atlantic from a few 

 degrees north of the equator to 

 about the 27th or 28th parallel. The 

 effect of this steady pressure, all in 

 one direction, over so enormous an 

 expanse cf water may be imagined by 

 those who have at all paid any atten- 

 tion to such subjects : there is an 

 abnormal elevation of the water on 

 the North-east coast of South Ame- 

 rica, to the height of (I believe it 

 has been calculated) thirty feet. 

 Literally, we have the " Atlantic 

 Steep," of Thackeray's well-known 

 verse. This enormous accumula- 

 tion of water streams off north- 

 wards, until, released from the pres- 

 sure of the trade-wind, but still 

 retaining its northern impetus, it 

 trends to the North-east — towards 

 our own shores, Iceland, and even 

 Spitzbergen. 



This slight outline will suffice to 

 show how the N.E. trade-wind is 

 the moving cause of the Gulf Stream; 

 and now I hasten to the next link in 

 the chain of cause and effect. What 

 causes the N.E. trade-wind? 



Most geographers, I believe, will 

 reply without hesitation, "Mainly 

 the Sahara," but let us see how. The 

 air throughout the whole of the tro- 

 pics being heated, and thus rarefied, 

 ascends into the higher regions, and 

 its place is supplied by the colder 

 atmosphere streaming in from north 

 and south. This simple statement, 

 however, requires, of course, many 

 modifications. I must confine my- 

 self to two immediately connected 

 with our subject. The first is this. 

 As the air streams in from the Arc- 

 tic regions where the velocity of the 

 earth on its axis is small, to the tro- 

 pical regions where it is consider- 

 able, it is obvious that the motion 

 of the earth from W. to E. being 

 only partially communicated to the 

 air, the latter will be left behind as 

 it were — that is, there will be an 

 apparent motion in it from E. to W. 



