PREFACE. 
I am often asked why, having passed my life till nearly threescore and 
ten in geological work, I turned to archeology, and what led me to choose 
remote Central Asia as a promising field. To answer this fully here would 
carry me beyond the restricted limits of a preface; I shall therefore state the 
reasons as briefly as possible. 
My geological explorations through Central and Northern China and 
Mongolia during 1863 had given me a great amount of material towards a 
skeleton geological map of the Chinese empire. I learned then that the 
successive dynasties had caused to be made exhaustive reports on the 
resources of the empire, covering not only those of the vegetable kingdom 
and the exact localities of all useful minerals, but including also fossil bones 
from caves in limestone, as well as certain fossil shells of well-defined species, 
both of which classes of objects belong in the Chinese materia medica. ‘Topo- 
graphical phenomena of extraordinary interest were also recorded. ‘These 
printed ‘“‘geographies’’ formed a great number of volumes. Here was a 
great mass of information adapted to supplementing the material I had 
gathered on my journeys. To utilize it I employed for several months three 
able native scholars, courteously found for me by the foreign office, to extract 
all items of a long series of classes of entries. The voluminous notes thus 
obtained were kindly translated for me by Mr. S. Wells Williams, then 
Secretary of our legation, aided by some of my missionary friends, and 
from them I was able to fill in my skeleton map and construct a “‘hypo- 
thetical geological map”’ of China, which Baron von Richthofen, in publish- 
ing the results of his later and far more extensive explorations, was good 
enough to say was remarkably good in its broad outlines. Extracts were 
made also from other works, and from maps, including even commented 
volumes of the writings of Confucius. 
In studying all this material I was naturally struck, as I had been on 
my journeys, by the great contrast between fertile China and arid Mongolia, 
and by the reaction of the latter upon the former as shown in the repeated 
attempts of vast Turanian hordes from the Mongolian table-land to overrun 
China. I was impressed, too, by a note on a Chinese map of the Tarim 
basin stating that here a large number of cities (between 100 and 200, I 
think) were buried by sand in the early centuries of our era. Then, too, on 
native Chinese maps the desert of Gobi or Shamo was called Han-hai (dried 
sea), and was by native writers said to have been formerly an inland sea, 
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