DEPARTMENT OE GEOLOGY 39 
There are also exhibited in a case in the hall three maps 
illustrating special phases of topography as follows : Map of a 
portion of the Catskill mountains, showing “stream robbing,” map 
of a portion of the valley of the Illinois river near Ottawa, 111., 
showing the work of a young stream, and a map of a portion 
of the Missouri River Valley near Marshall, Mo., showing a 
typical flood plain. All these maps are on the horizontal scale 
of an inch to a mile and with either no vertical exaggeration or 
one of twice the horizontal. 
A number of large geological photographs are exhibited on a 
stand in the hall. 
There is also exhibited a model on a large scale of the 
Chandler iron mine, Ely, Minnesota. It illustrates how the under- 
ground workings of a large mine are carried on. Two shafts 
(shown at the rear of the model) run from the surface down- 
ward. At levels 60 feet apart, horizontal galleries run from the 
shaft and connect at intervals with other passages. From the 
two main galleries, sloping ways, not shown in the model, lead 
upward to passages at higher levels which do not connect with 
the shaft. Here as the ore is excavated it is thrown through 
chutes to the tramways of the main galleries, and there taken 
by ore cars to the shafts and raised to the surface. The timber- 
ing is to prevent the top and sides from caving. 
Upon the wall is a large painting representing a section of 
the Soudan mine of Tower, Minnesota. 
Hall 77. 
Passing into Hall 77, and turning to the right, maps will be 
found against the wall in the following order : 
Relief map of the Isthmus of Panama, showing the proposed 
course of the canal. 
Map of the Isthmus of Panama. 
Model showing methods of irrigation on steeply and gently 
sloping fields. 
Relief map of the drainage basin of the Arkansas river in 
Colorado, showing the relations of the catchment basins to the 
reservoir sites and irrigable lands. The entire area drained by 
the Arkansas river from its source in the High Rockies to the 
plains of eastern Colorado is shown. 
