MILPA AGRICULTURE—COOK. 817 
of protection implies a rather advanced state of social organization, 
something that might correspond to the colonizing policy of the 
Incas of Peru, in withdrawing people from congested districts and 
sending them to unoccupied regions. 
A precaution observed at the present day by some of the Indians 
of eastern Guatemala may: have been practiced more widely in 
ancient times. In passing through the district between Cajabon and 
Lanquin, in the valley of the Cajabon River, in May, 1914, when 
farm-burning operations were in progress, it was noticed that a 
method of fire protection had been applied. Many of the clearings 
were surrounded by barriers made by removing all the branches and 
dry leaves from the ground along a strip 2 or 3 rods wide, which 
serves to stop the fire at the border of the clearing instead of allow- 
ing it to sweep over the neighboring lands. 
The use of this expedient by the ancient Mayas would have enabled 
them to lengthen the period of agricultural occupation beyond what 
might have been possible under the simplest forms of milpa agricul- 
ture. According to Morley, who has deciphered the date signs on 
many of the ancient monuments, the period of occupation of some 
of the Maya cities appears to have extended over nearly four cen- 
turies, though others seem to have been inhabited for only a few de- 
cades. The nature of the soil is, of course, a primary factor in de- 
termining how long the land can be cultivated by any system of 
agriculture, but the making of fire-stops around the clearings of each 
year undoubtedly would conserve the fertility of the country and 
enable it to support a larger population for a longer period. 
That other expedients may have been used by the ancient Mayas is 
hardly to be denied in the present state of knowledge. Several 
rather specialized systems of agriculture were developed in the 
neighboring mountains and plateau regions, where languages of the 
Maya stock are still spoken. Different forms of ancient agricul- 
tural terraces are found in several districts in Guatemala and south- 
ern Mexico, none as carefully constructed as those of Peru, but 
sometimes covering large areas, as in the region of Comitin and 
Ocosingo in southern Mexico. Terraces, with retaining walls of 
rather rude stonework, are found in many of the mountain valleys 
in eastern Guatemala, usually at altitudes of 2,000 to 3,000 feet, but 
some of them as low as 700 feet. In the eastern valleys of Peru 
most of the terraces are at altitudes between 12,000 and 6,000 feet, 
with little or no terracing below 5,000 feet. 
Though the agricultural period might be lengthened for several 
generations by using the fire-stops, the natural limitations of the 
milpa system would be reached eventually. Population would need 
to be restricted as well as fires if a permanent balance were to be 
