90 IOWA ACADEMY OF SCIENCE 



aceous shale. In some places the movements have resulted in the coal 

 being intimately mixed with the rocks of the roof and the floor. The 

 roof and the ^floor are most commonly of shale. One sometimes 

 finds the roof to be of shale and the 'floor of sandstone, or vice versa ; in 

 a few places sandstone forms both the roof and the floor. The roof is 

 frequently fractured to such an extent that, in mining, timbering will 

 be necessary. 



The coal of the region is of good quality, the best grade being anthra- 

 cite, the lowest grade semi-bituminous. The average of 32 analyses 

 of samples of coal taken l)y Dr. Martin so as to represent the coals of 

 the whole field was as follows : 



Per Cent 



Total moisture 6.02 



Volatile combustible 10.44 



Fixed carbon 75.30 



Ash 8.23 



Sulphur 1.47 



The fuel ratios of these coals varied from 3.61 to 15.88, the average 

 being 7,78. The highest B. T. U. value was 15,574, the lowest 8,386, and 

 the average of the 32 analyses was 13,174. The average analysis of 7 

 of the coals which were classed as anthracite was: 



Per Cent 



Moisture 7.88 



Volatile combustible 6.15 



Pi^ed carbon 78.23 



Ash 7.74 



Sulphur 1.30 



The semi-bituminous grade of coal is found in the southwestern part 

 of the field, the anthracite in the northeastern. Between these two areas 

 the grade of coal is intermediate between semi-bituminous and anthra- 

 cite. The distribution in the grades of coal corresponds somewhat 

 closely to the complexity of structure in the different parts of the field. 

 The structure becomes more and more complex from tlie southwest 

 toward the northeast. The grade of the coal has been made better with 

 an accompanying complexity of structure. 



The semi-bituminous coal has been shown to possess good coking 

 properties. 



A striking feature of the coals, and one which is likely to be a serious 

 handicap to their utilization, is their crushed and sheared condition. In 

 many of the surface exposures and in the tunnels, drifts, and open cuts, 

 where development has been carried on, the coal is soft and friable. 



