868 



SCIENCE. 



[N. S. Vol. XXIII. No. 597. 



pei-iods have not been definitely observed. 

 Inferential data have been secured from ex- 

 ploration in the ancient ruins that render 

 it possible to explain the migrations of 

 early populations. 



The conditions of the environment briefly 

 recapitulated are: 



1. A plateau of considerable elevation 

 isolated geographically. 



2. Slight rainfall, locally distributed; 

 absence of cloud blanket; excessive light, 

 radiation and evaporation; high winds, 

 dust storms; rarefied air. 



3. Forested mountains, plains with xero- 

 phytic, hydrophytic and halophytic vege- 

 tation; plant colonies; desert animals. 



Within this general enclave we have sev- 

 eral subenvironments which may be con- 

 sidered from the point of view of the avail- 

 ability for habitation by man. 



Suh environments : 



1. Prohibitive to man and in great de- 

 gree to animal and vegetal life. 



2. Precarious except to man in low grade 

 of culture, as roving, hunting and primi- 

 tive tribes. Animal and vegetal life suffi- 

 cient. 



3. Habitable by man acquainted with 

 agriculture, but more or less precarioiis. 



4. Favorable for agriculture and pro- 

 duction of economic surplus. 



The subenvironments more favoring in 

 the struggle for existence are : 



1. Mountains at sources of rivers. Here 

 are narrow valleys for agriculture with oc- 

 casional irrigation; game, nuts, fruits and 

 plants; timber, building material, etc. 

 The tempei'ature cold, with short growing 

 season. 



2. High plateaus with marshes, lakes, 

 ponds. Land lying well for catchment of 

 water. Temperature as in 1. 



3. Mesa country, with broad plains and 

 valleys ; springs ; streams flushed at seasons. 



4. Riverain lands in lower stream valleys 



suitable for irrigation by canals or warp- 

 ing. 



The effect of this environment upon 

 plants is to reduce them to their lowest 

 terms; animals, to modify them in impor- 

 tant ways ; man, to subject his mind to the 

 stress of severe conditions, reactuig notice- 

 ably on his body, and mightily on his 

 thought and material progress. 



The environment was suitable, or extinc- 

 tion of tribes followed or a movement was 

 made to a new subenvironment. Thus the 

 constant and seemingly erratic migration 

 of tribes which have covered the Pueblo 

 region with remains of ancient towns may 

 have been due to natural causes which dis- 

 environed them, such as earthquakes, fail- 

 ure of springs, etc. The final localization 

 of the Pueblos is an index, in large meas- 

 ure, of the regional fitness. 



It is probable that the tribes coming into 

 the pueblo environment were at first con- 

 fined to mountain regions where there is a 

 permanent water-supply and natural sub- 

 sistence, and that gradually they spread 

 along the watercourses and into all the 

 subfenvironments. "With the increase of 

 population, the building of permanent vil- 

 lages of stone, the beginning or extension 

 of the agriculture of maize, which cereal is 

 a major factor in the distribution and per- 

 manency of tribes, the settlement of the 

 Pueblo region went on apace. 



It is apparent that in the advanced cul- 

 ture stage of the Pueblos the i^rivations 

 of environment had less resti'ietive char- 

 acter than in earlier stages. Gradually 

 they attained superiority to the environ- 

 ment which had worked on them to the 

 extent of its capabilities, and this has been 

 the histoiy of the growth of mankind. 



Thus the regions least favored, in fact 

 prohibitive to tribes who had not the school- 

 ing of experience, became the seed-fields of 

 advanced tribes. Given unfailing springs 

 as a starting point, the waste sand flats of 



