108 CLASSM'iCATION 01' IfiE PUBLIC LANDS. 



quantity of heat given off by the burning of the coal is determined 

 by multiplying the product of the weights of the metal and water 

 in the apparatus and their respective specific heats by the rise in 

 temperature. The result thus obtained is calculated into terms of 

 calories and British thermal units. 



PREPARATION OF MATERIAL. 



The preparation of material by the field man, so that it may be 

 considered to the best advantage in the work of classification and 

 valuation, has already been considered in the chapter entitled " Prepa- 

 ration of data for classification," immediately preceding the discus- 

 sion of the classification of coal lands. 



PROCEDURE IN CLASSIFICATION AND VALUATION. 



In the actual work of classification of coal lands each area under 

 consideration must be treated individually, yet in general a definite 

 line of procedure is followed. 



The first step is to assemble all the available data, including not only 

 the maps and reports of the geologists who may have made a special 

 examination of the field, but the reports of any special agents of the 

 Land Office who have been in that field, as well as all reports of 

 geologists who may have visited the field at some earlier time (prob- 

 ably for some other purpose) and all other available information 

 concerning the land or the coal it may contain. The land-classifica- 

 tion board has a system of graphic records which show at once the 

 existence of any reports on the field and give references to them, so 

 that when the case is taken up all the data available are at hand. As 

 a matter of fact the field man will usually have familiarized himself 

 with all these earlfer data and will be prepared to present them as 

 may be necessary. 



The second step is to scrutinize carefully all these data, and by their 

 aid to take the action or to obtain the information listed under the 

 following heads: 



1. The number, names, character, and other features of the coal- 

 bearing formations are determined. As most of these formations 

 extend over large areas, some of them crossing several States, a gen- 

 eral knowledge of the formations at once suggests the probable con- 

 ditions to be found in the field studied, and that general Imowledge 

 may strongly affect the action to be taken in classification and 

 valuation. 



2. The number of coal horizons or groups of horizons is 

 ascertained. 



3. The thiclniess of each coal bed over the field is determined, if 

 it can be traced. If each bed can not be traced the group of coals 



