IOWA ACADEMY OF SCIENCE 91 



even where fairly firm and iinbrolfen masses of coal are found, they can 

 be readily crushed. It is difficult to find large lumps of coal free from 

 fractures and slickensided surfaces. When being mined, such coal can- 

 not escape being badly broken, and the difficulties of shipping will be 

 great. In the case of the anthracite, the crushed and friable condition 

 is likely to impair seriously its market value. With regard to the grades 

 of coal of coking quality, the soft character may not be serious in that 

 the coal can be converted into coke before shipping. It is scarcely 

 probable, in a region where the crustal movements have been so wide- 

 spread and intense, that the coals below the zone of surface disintegra- 

 tion will be free from the crushed and fractured conditions which are 

 so prevalent at and near the surface. 



Gas has been found in several of the tunnels, hence, in mining, safety 

 devices will be necessary. 



Development. 



At more than three hundred places within the field, more or less 

 development work has been done. But no extensive mining has been 

 carried on. The most prevalent kind of work consists of small surface 

 openings. However, more than thirty drifts or tunnels have been run 

 with an aggregate length of more than three thousand feet. The most 

 systematic development work has been done on the Cunningham, the 

 Controller Bay, the English Company, and the Davis groups. On the 

 Cunningham claims several long tunnels have been run. At the Mc- 

 Donald mine on the Controller Bay group is a working drift more than 

 six hundred feet long. On the claims of the English Company there are 

 three tunnels with a total length of more than nine hundred feet. On 

 the Davis group is a tunnel of more than five hundred feet. During 

 the summer of 1910, the Davis group was the only one in the field upon 

 which systematic development work was being carried on. 



Summary and Conclusions. 



The coals of the Bering River field are of good quality and the ton- 

 nage is unquestionably great. But the probable amount of this coal 

 which is avaiable at present or which will be available in the near future 

 cannot be stated with any degree of reliability. The conditions of 

 occurrence are such that, until extensive development has revealed many 

 data at present unknown, an estimate of the available coal would be 

 little more than a guess. In coal fields of somewhat simple structure, 

 fairly reliable estimates may be made of the available coal from a study 



