PREFACE. XXXV 
Lastly, at Merv and Samarkand Mr. Homer Kidder rendered valuable 
volunteer assistance. 
It should be mentioned that the topographic work was executed on a 
plane-table with telescopic alidade specially constructed by Messrs. Buff & 
Buff. 

To avoid misunderstanding it may be added here that the word culture is used as a 
synonym for crvilization, and that the term culture-strata (Kulturschichte of the Germans) 
stands for the débris slowly accumulated during occupation of an inhabited site. 
It should also be added here that I presented the outlines of our results in my presi- 
dential address at the Ottawa meeting of the Geological Society of America in December, 
1905; and that some changes from that address, in connection with the question of culture 
gaps and datings, are due to later and more extended analysis. 
It is desirable to refer here to a point that was overlooked on pages 55 and 56, in 
advancing a law of vertical growth of sites built of air-dried bricks. It is this: Aside from 
the contribution of bones and potsherds, the accumulating débris is derived chiefly from 
the wasting surface of roofs and walls. This is roughly proportionate to the area of these 
surfaces. In primitive and small sites the houses had, as a rule, only one story, but in 
larger cities of advanced culture, such as were Merv and Memphis, houses of two or more 
stories were frequent, and the rate of growth was correspondingly much more rapid. 
es 
DuBLuin, N. H., October 1, 1908. 
