43 
tions of the primeval crust. Others, however, regard granites 
as the last term in the metamorphism of such rocks, and for" 
that reason the gneisses have been placed in juxtaposition to 
them. Varieties of gneiss, based upon the prevailing mineral, 
whether biotite, muscovite, hornblende, or others, are includ^^' 
here. 
HALLS 76 AND 77. 
QfiOQRAPHIC GEOLOGV. 
The purpose of this collection is to illustrate in a vivid 
and realistic way the surface configuration of the earth. The 
chief feature of the exhibit is a series of relief maps which 
reproduce on as natural and representative scales as practica- 
ble, the topography and structure of selected portions of the 
earth s surface. A part of the series shows only topography 
and sculpture, while another part shows geological structure as 
well as topography. To some extent, the topography is shown 
on one map and the geological structure on another, so that 
both elements are represented with the greatest distinctness. 
The portions of the surface selected to be represented are usu- 
ally such as to portray some typical form of surface sculptur- 
ing or of volcanic accumulation. Some, however, represent na- 
tural or political divisions. 
In addition to the relief maps, there are models showing 
geological structure or illustrating methods of development. 
Some of these are dissected so as to show the more intimate 
structure of the formations. There are also exhibited globes, 
wall maps, and other geographic material. The following is a- 
list of the principal features : 
HALL 76. 
Entering this hall from the West Dome and passing around 
to the right, the maps against the wall will be found in the fol- 
lowing order : 
Relief map of Kentucky showing topographical and geologi- 
cal features and location of principal coal fields. 
