INDIAN AMERICA 247 
(6) Chinampas. These so-called floating gardens are actually 
artificial islands built near the shores of shallow lakes by piling up 
layers of aquatic plants and silt from the bottom of the lakes. The 
porous soil of the chinampa is perpetually moist as a result of the 
infiltration from the surrounding waters. Additional moisture is 
applied directly to the individual plants by lifting water manually 
from the canals surrounding the plot, by means of long-handled 
cloth buckets. As the water is muddy, this amounts to the addition 
of new soil. Furthermore, aquatic plants and other fertilizers are 
used. 
The Indian methods of land reclamation and soil conservation 
also included various types of adjustments to farming on slopes, 
these are: 
(a) Rock walls built on the contour to form level benches irri- 
gated with elaborate aqueducts, as were the gardens of the Tex- 
cocan king Nezahualcoyotl (fifteenth century). Actually, the 
royal gardens were only a part of an extensive project of land 
reclamation through terracing and irrigation in the foothills of 
the mountains to the east of Texcoco. There is an early colonial 
document concerning the water rights of the Indian farmers culti- 
vating the reclaimed lands. Later, the upper aqueducts and some 
of the terraces were abandoned and erosion carried away the soil 
on the top of the hills. However, the middle and lower level ter- 
races are still well kept and cultivated. 
(6) Rain farming terraces. (1) With retention walls—the distri- 
bution of these extended from the valley of Mexico to British 
Honduras. Most of them are now abandoned; (2) without reten- 
tion walls but hedged with maguey—these are built to reduce slope 
gradients, to retain soil and moisture. This system is widely 
practiced at present in Central Mexico. 
Although fairly widespread, the techniques of soil conservation 
were by no means universal in pre-Columbian Mexico. There is 
no doubt that in many districts the exploitation of land might 
have resulted in serious depletion and destruction of soils, but the 
wholesale damage seems to have been a result of the technological 
changes introduced with the Spanish Conquest. In the first place, 
large-scale mining operations demanded huge quantities of wood 
for timber and fuel, thus bringing about the destruction of forests, 
