332 THE POPULAR SCIENCE MONTHLY. 



nution of evaporation, may have been immense. Under such circum- 

 stances, it is easily conceivable that a swift and voluminous torrent, 

 periodically swollen by the contributions of the great southern afflu- 

 ents, covered the delta with a permanent inundation, and swept down 

 gravel and bowlders into the lowest part of its course. 



That the outflow of the Nile once extended far beyond its present 

 limits appears to be certain, for a long, deep, dry valley so like an 

 ancient river-bed that the Arabs call it the Bahr-bela-Ma, or waterless 

 river runs from south to north in the Libyan desert along the west- 

 ern edge of the delta, and ends in the Mediterranean shore beyond 

 Taposiris, far to the west of the Canopic mouth, the most westerly of 

 the outlets of the Nile known during the historical period. And, in 

 the extreme east, far beyond the most easterly arm known to the 

 ancients in fact, in the middle of the Isthmus of Suez, about Lake 

 Timseh alluvial deposits, containing Nile shells and hippopotamus- 

 bones, show that the Nile once extended into this region, and perhaps 

 poured some portion of its waters into the Red Sea, by way of antici- 

 pating the engineering operations of more modern days. 



These facts tend to show that any calculation of the age of the 

 delta, based upon the present action of the Nile in the way indicated, 

 may need to be abbreviated. But, on the other hand, there are many 

 obvious considerations which tend the other way. 



It is easy to see that the time required for the deposition of a cer- 

 tain thickness of alluvial soil, in any one part of the delta, can only be 

 a measure of the time required to fill up the whole, if the annual sedi- 

 ment is deposited in a layer of even thickness over the entire area. 

 But this is not what takes place. When the river first spread out from 

 the southern end of the delta, it must have deposited the great mass 

 of its solid contents near that end ; and this upper portion of the delta 

 must have been filled up when the lower portion was still covered with 

 water. And, since the area to be covered grew wider, the farther 

 north the process of filling was carried, it is obvious that the northern 

 part of the delta must have taken much longer to fill than the south- 

 ern. If we suppose that the alluvium about Memphis was deposited 

 at the rate of one twentieth of an inch per annum, and that there are 

 fifty feet of it, ten thousand years may be the minimum age of that 

 particular part of the delta ; but the age of the alluvium of the delta 

 as a whole must be very considerably greater. And indeed there are 

 some indications that the shore-line of the nascent delta remained, for 

 a long time, in the parallel of Athribis, five-and-twenty miles north of 

 Cairo, where the remains of a line of ancient sand-dunes are said to 

 attest the fact. Hence, all attempts to arrive at any definite estimate 

 of the number of years since the alluvial plain of the delta began to 

 be formed, are frustrated. But, the more one thinks of the matter, the 

 more does the impression of the antiquity of the plain grow ; and 

 I, for my part, have no doubt that the extreme term imagined by 



