32 Field Museum of Natural History — ^ Reports, Vol. IV. 



within. From the bin two chutes lead to the two ten-stamp mills 

 which are the prominent features of the model. Each mill, exclusive 

 of its concrete foundation, is one foot high and ten inches long. Each 

 consists of a heavy oak framework which supports ten steel stamps 

 working upon steel anvils in a wooden mortar equipped with copper 

 screens. The shaft, cams, and tappets are all of steel while the boxes 

 in which the journals run are, like those of the full-sized mills, of cast 

 iron. The flywheel, which is of wood, is driven from a main driving shaft 

 by a leather belt. In one mill the screens in front of the mortar are 

 shown removed to permit a view of the interior. In front of the mill 

 are shown amalgamated copper plates and a launder. The entire model 

 has been built according to the plans and specifications of a standard 

 mill and has been modified only in such ways as the small size has 

 made necessary, or as changes were required in the relative positions 

 of the parts in order to place the model within the space available. 

 The mill has been so constructed that if power were available, it could 

 be run daily without injury, and with a few inexpensive alterations it 

 could be rendered capable of actually treating ore. Another model 

 constructed in the Department and installed in a fioor case in this 

 Hall represents a Hartz jig of standard type. Owing to the scarcity of 

 space the model was made upon a small scale, although the details of 

 its structure are complete. The height of the model is six inches, 

 length eight inches, and width four and one-half inches. It is built of 

 wood except the shafting, wheels and eccentrics, which are of steel. 

 The jig is represented as treating a low-grade silver ore, taking the 

 ground ore and yielding three products, gold ore, silver ore, and waste. 

 Like the ten-stamp model this jig is a working model which upon the 

 application of power could be run continuously. In fact the ore beds 

 shown with the model were made by the operation of the model itself. 

 Maps of Colorado and Nevada showing the localities and names of the 

 gold and silver mining districts of those states were prepared by the 

 Assistant Curator and placed upon the walls of the Hall adjacent to the 

 corresponding collections. The work is intended to be continued until 

 all the important mining localities shall be represented. In Halls 76 

 and 77 the large maps of the Grand Canyon, Eureka Basin, and Auvergne 

 have been framed, and the large photograph of Miles Glacier presented 

 by L. V. Kenkel has been framed and placed on exhibition. There 

 have also been framed and installed in Hall 77 the recently purchased 

 maps of Illinois and the Malaspina Glacier. It was found that the screws 

 used to hold the case sashes in place in Skiff Hall were working loose owing 

 to the wear of the wood. Accordingly metal sockets were provided for 



