CLASSIFICATION OF MINERAL LANDS. 99 



I.OCATIOIT. 



In work done for classification all the points or features concern- 

 ing which information is obtained in the field must be accurately 

 located with reference to the land lines, for if locations are not 

 exactly specified the information is of little value. For example, a 

 geologist may study an outcrop of a 30-foot bed of coal, measure its 

 sections, photograph it, and sample and analyze the coal to determine 

 its quality or test it in any other way, but if, when he has done all 

 these things, he can not tell whether the outcrop is in sec. 31 or sec. 

 32 of a given township, the information he has gathered is entirely 

 valueless for purposes of classification. It is therefore necessary 

 that all the features to which his information relates be accurately 

 located on his field maps, with special reference to township and 

 range lines, section lines, and quarter-section lines, and even accu- 

 rately within the 40-acre tracts, as it is desirable to know exactly 

 how many acres of the forty are underlain by coal in order to 

 determine the value of that particular forty. The methods of survey 

 by which the geology is tied as accurately as possible to the public- 

 land net have been described in a preceding chapter. 



STBATIGBAFH7. 



The first purpose of gaining a thorough knowledge of the stratig- 

 raphy is to be able to recognize groups of rocks that are coal bear- 

 ing elsewhere or to recognize other rocks that the wide experience 

 and knowledge now available concerning the geology of the 

 Western States have shown not to be coal bearing. The second 

 I)urpose is to determine, from such data as may be obtained on the 

 surface, the " lay " or structure of the coal-bearing formation and 

 the groups of coal beds it contains. 



Just as in the Eastern States it has been found that workable 

 coal beds are confined to a particular part of one large gEOup of rocks, 

 which has long been designated the " coal measures," so in the West 

 it has been found that workable coal beds are confined to relatively 

 few groups of rocks, which are separated usually by great thicknesses 

 of other rocks that are nowhere known to contain workable coal beds. 

 As the sedimentary rocks of the West consist mainly of sandstones, 

 shales, and limestones, those of like lithologic character being simi- 

 lar to one another in general appearance, the particular sand- 

 stones and shales with which the coal beds are associated can 

 iis a rule be distinguished only by means of the fossil plants or 

 animals that are associated with them. Thus it has been found 

 necessary to employ the services of several experienced paleontolo- 

 gists to examine the fossils associated with the rocks and from 

 these fossils to determine the age of coal-bearing formations. 



