4t 
486 NOTES OF A BOTANIST chap. 
from any accidental hollow at first — and then con- 
tinually deepened by the pebbles and sand whirled 
round and round in them by the surging and eddying 
waves of the cataracts during the season of flood/ 
Although we have no elements wherefrom tO' 
determine positively the date and mode of execution 
of the picture-writings, those questions seem to me 
to have been involved in unnecessary mystery. 
The instruments used in scraping such deep lines 
in the granite were probably chips of quartz crystal, 
which were the hardest cutting- instruments pos- 
sessed by the aborigines of South America. In 
the Amazonian plain I know of but two extensive 
deposits of large rock-crystals — one of which is a 
good way up the Rio Branco, and the other is at 
the foot of Mount Duida, near the village of Esme- 
ralda, therefore in the immediate neighbourhood of 
the Casiquiari. I know also of but one such deposit 
on the Pacific side of the Andes, namely, in the 
hills of Chongon near Guayaquil ; yet pieces of 
quartz, some of which have served as knives, others 
as lance- or arrow-heads, are found strewed about 
the sites of ancient towns and settlements through 
several degrees of latitude. Whatever the instru- 
ment used by the Indians of the Casiquiari, it is 
difficult to assign any limit to the time required for 
the execution of the figures ; but any one who has 
seen an Indian patiently scraping away for months- 
at a bow or a lance before bringing it to the desiredi 
symmetry and perfection, or who knows that it has 
taken a lifetime to fashion and bore the white 
^ [The supposed tracks of animals are doubtless works of art like the othef 
figures, probably due to a desire to imitate the well-formed impressions of feet 
that the hunter must continually meet with during his search for game. — Ed.] 
