33 ° CAVE AND CLIFF DWELLERS. 
done by machinery. In some places 
there were evidences that they had 
heated the stones by fire and had 
then thrown water thereon, shivering 
the front by sudden chilling, a method 
yet employed in Honduras and Guate¬ 
mala, according to an engineer at Bato- 
pilas who had recently arrived from those 
countries. 
One of the most singular things 
connected with prospecting in this par¬ 
ticular portion of the mountains is the 
means by which large deposits of silver 
near a tunnel can be located. If an 
iridescent, smoke-like appearance spreads 
over the rocks at any point of a new 
tunnel or drift at the end of a week or 
two, the engineers always drift for it and 
generally strike silver. This stain is 
called by them “ silver smoke,” and is 
