CLIMATE OF NORTH AMERICA HUNTINGTON, 397 



parts of the nrid soutlnvost or in Mexico, they built u considerable 

 number, partly close to their main \T.llago, ]>iit cliiefly on a slope of 

 especially favorable location. This in itself may seem of small 

 importance, but it is significant as indicating that probably the 

 population was decidedly dense. Had there been abundant unused 

 irrigable land either in the Jlincon Valley or in neighboring regions, 

 the Hohokam woidd scarcely have gone to the labor of building ter- 

 races. Hence we infer that the population of the country as a whole 

 was as dense as is indicated by the abundant ruins. 



The preceding pages have been devoted to the description of the 

 phenomena of a single valley in southern Aiizona. That valley was 

 not chosen because of the strength of its evideiices of climatic changes, 

 but merely because it happened to be the fii'st v/hich I investigated 

 and the one where I spent most time. Half a dozen others might 

 have been chosen equally well. The same type of phenomena is 

 displayed with equal clearness in the Altar Valley of northwestern 

 [Mexico, in the Chaco Valley, 500 miles to the northeast, in the north- 

 western corner of the State of New Mexico, and in numerous valleys 

 between the two, and in the regions round about. Further details, 

 however, would overcrowd this article and we must hasten on to 

 consider another phase of the subject. 



PART II. THE SUCCESSION OF CIVILIZATION. 



Thus far we have dealt solely with the question of whether the 

 climate of the past was different from that of the present. Having 

 concluded that there is strong evidence that this was the case, we 

 shall now attempt to ascertain whether the change from the past to 

 the present took place gi'adually or in pulsatory fasliion, and whether 

 its various phases synchronize with similar phases in the Old World. 

 The first evidence on this point is derived from alluvdal terraces and 

 lacustrine strands, and points distinctly toward pulsatory changes, 

 but gives little clew to their dates. Coming to man's worlcs, we find 

 that a broad view of the ruins of the southwest seems to show that 

 they belong to at least three periods. During each of these periods 

 the area capable of cultivation appears to have been more extensive 

 than at present, although only slightly so in the last period. In the 

 mitldle period the arable area was larger than in the last, and in the 

 earliest still larger. The last period dates back only to Spanisli 

 times. The best example for discussion here is the ruins of Gran 

 Quivira in central New Mexico. These ruins lie on the top of a 

 rounded liill about 200 feet above a broad, open vallo}'- draining 

 toward the south and a mile or more in width. The altitude of the 

 region is over 6,000 feet, so that the temperature is coinparatively 

 low. The ruins consist of two distinct i)ortions, Pueblo and Spanish, 

 covering an area about 700 by 350 feet. ^Ul the buildings were con- 



