GRASSLAND AND FARMLAND—SMITH 361 
and the hen gave eggs without man having to seek the nests of wild 
birds in the forest. The new environment produced by the stimulus of 
crops, domestic animals, and larger residence groups seems to have pro- 
duced a mental emancipation that gave new freedom to the inventive 
type of mind. 
‘A NEW ERA, BASED ON LARGER HUMAN GROUPS, HAD ITS ORIGIN IN 
THE PERMANENT FERTILITY OF THE IRRIGATED VALLEYS OF EGYPT, 
MESOPOTAMIA, AND THE INDUS 
In Egypt, Stone Age man found that the recurring floods fertilized 
his land each year with a thin but rich crust of mud. As a result he 
could stay in the same place generation after generation. Large settle- 
ments soon developed. 
This was something new in the world. Revolutions emerged from 
it. Gradually many little governments came under one ruler, the gov- 
ernmental unit grew until finally the prowess of one ruler brought all 
Egypt, with it millions of people, under one government. For 6,000 
years the Nile Valley has continuously supported its heavy population 
by benefit of the annual automatic deposit of mud. The Nile is the 
most regular, most orderly, most easily usable large river in the world. 
It has well earned the affectionate name of “Father Nile.” Large 
areas of swamp along its upper reaches become automatic reservoirs 
that tame the sudden floods that trouble the lower valleys of most 
rivers. 
The fertility of the irrigated lands along the Tigris and Euphrates 
was replenished in somewhat the same way. But, as compared with the 
Nile, the Tigris and Euphrates are wild and disorderly rivers. They 
have no controlling reservoirs. The maintenance of irrigation in 
Mesopotamia required more labor than in Egypt, and a continuously 
effective social organization was necessary. Like Egypt, Mesopotamia 
supported heavy populations, towns, cities, kingdoms more than 5,000 
years ago. 
The recent excavations of Mohenjo-daro and neighboring cities 
on the lower Indus show somewhat similar developments about the 
same time. These three populous valleys supported themselves by ir- 
rigation on wide-spreading alluvial lands with a dry, warm climate. 
Man has not yet imagined better conditions for agricultural production. 
In these hot, dry valleys men lived under the compulsion of the need 
to work their crops in a season of flowing water, and under the near- 
compulsion of leisure in the season of drought. There was also the 
further compulsion of governments. These factors of surplus food, 
leisure time, large business enterprises, the desire for self-expression, 
and the compulsion of strong government produced writing, libraries, 
codes of laws, pyramids, and temples—cultures that were in many 
