234 Proceedings of Eoyal Society of Edinburgh. [sess. 
pologists divide them into four divisions, representing as many 
progressive epochs, under the names of the localities which have 
yielded the most characteristic specimens, viz., Magdal6nien, 
Solutreen, Mousterien, and Chelleen. The area of their distribu- 
tion is rapidly extending, and now embraces not only numerous 
localities throughout Europe, but several in Asia, Africa, and North 
America. But the special techniciae in their manufacture, though 
clearly showing a progressive skill, is of little value in deciding the 
question of their antiquity, as it might have been acquired in a few 
hundred years instead of as many centuries or even more. Hence, 
to assign a more definite meaning to the duration of the series of 
changes in this chronological sequence, the anthropologist has 
recourse to collateral sources of information. And this is one of 
the points in which the geologist comes so opportunely to his 
assistance. The latter takes no cognisance of the objects them- 
selves, but examines the gravel beds, or other localities, in which 
they were found, and so, on geological grounds, assigns to them 
a relative antiquity. Here, he comes to a bed of ancient river- 
drift, left high and dry many feet above the present highest flood- 
mark of the river, there, but still higher up the slope, another 
similar bed, both of which yield flint implements. These two 
gravel deposits are, of course, of different ages ; and so the geologist 
also comes to form a chronological scale based on the time the 
water has taken to excavate the valley. This is how Sir John 
Evans depicts the chronological element involved in this problem : 
— “ Taking our stand on the high terraces at Ealing, or Acton, or 
Highbury, and looking over the broad valley, 4 miles in width, with 
the river flowing through it at a depth of about 100 feet below its 
former bed, in which, beneath our feet, are relics of human art 
deposited at the same time as the gravels, which of us can picture 
to himself the lapse of time represented by the excavation of a 
valley on such a scale by a river greater, perhaps, in volume than 
the Thames, but still draining only the same tract of country ? 
“ But when we remember that the traditions of the mighty and 
historic city now extending across the valley do not carry us back 
even to the close of that period of many centuries when a bronze- 
using people occupied this island ; when we bear in mind that 
beyond that period lies another of probably far longer duration, 
