The whole district of Casas Grandes is further studded with artificial mounds, from which are excavated from time to time large numbers of stone axes, metates or corn-grinders, and earthern vessels of various kinds.
Corn grinders were flat oval stones, with a smaller one lying cross-ways (95), and slid from end to end.
The flint vase-grinders were used in the early dynasties (110), and also sandstone grinders for hollowing larger vases (III).
24), but more usually grinders blocks of quartzite sandstone (26-34), and occasionally Df diorite (Q.
The first compound miscroscope (discovered probably by the Middelburg lens-grinders, Johann and Zacharias Janssen about 1590) was a combination of a strong biconvex with a still stronger biconcave lens; it had thus, as well as the first telescope, a negative eyepiece.