NEW WORLD PALEO-INDIAN—ROBERTS 431 
human occupation. In fact some geologist think that the sand-gravel 
layer in which the Cochise material occurs may be a redeposition 
rather than an original flood plain and that the archeological speci- 
mens are later than the animal bones and gravel would indicate. If 
the widespread evidence for such a hiatus is correct, some explanation 
should be found for the break in continuity and for the possibility that 
the earliest migrants, like the animals they hunted, became extinct. 
On the other hand, if the first occupation was followed by uninter- 
rupted inhabitation, some good reason for the sterile stratum in so 
many sites should be forthcoming. One postulation has been that the 
break merely was in the plains and the southwestern area, where the 
increasing temperatures and progressive desiccation following the 
onset of the postglacial produced unfavorable conditions and forced 
the people on eastward and southward to other regions where they 
continued to live. Eventually, after an amelioration of the climate 
in their former habitat and an influx of new migrants who found it 
again suitable for occupation, their descendants came in contact with 
some of the later peoples and there was an intermingling that is chron- 
icled in the sporadic appearance of older physical types in recent 
groups. This is a logical explanation, but thus far the preponderance 
of archeological evidence is against it. 
LITERATURE CITED 
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CAMPBELL, ELIZABETH W. CroziER and WILLIAM H. 
1935. The Pinto Basin site. Southwest Mus. Pap., No. 9. 
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