12 Field Museum of Natural History 



tendency to move, consists of a continuous system of 

 hollow squares framed from heavy timbers. In this 

 mine these squares are ten feet on edge but under 

 worse conditions, they have to be made much shorter. 



Henry W. Nichols. 



This model is exhibited on the second floor of the Museum in 

 an alcove in Frederick J. V. Skiff Hall. 



[12] 



