22 INTRODUCTION. 



per-oxide of iron, or simple iron-rust held in suspension in the 

 water of springy places, and which impregnates the wet earth 

 aronnd the place where the water issues. So far as the pre- 

 sence of this substance is concerned, it amounts only to this : 

 the strata associated with Ibeds of coal, and also the coal 

 itself, almost invariably contains more or less iron, which 

 becoming oxidized, passes out with the water and is deposi- 

 ted upon the surface, where, from its conspicuous appearance, 

 it always attracts much attention. While this appearance of 

 iron is almost invariably present with coal and its associated 

 strata, it is equally true that very many other strata which 

 have no possible connection with beds of coal, also contain 

 iron in similar form and in as great abundance; and it also 

 produces the same appearance at the surface which that of the 

 coal strata does. 



The popular belief that the presence of any particular 

 substance upon or near the surface, invariably indicates the 

 presence of a bed of coal beneath, or associated with it, is 

 erroneous. As to the relative position of coal-beds with 

 other strata, the rule is that a bed of clay, commonly called 

 fire-clay, underlies each bed of coal; and a bed of shale, 

 popularly called soap stone, overlies it. Sometimes, however, 

 sandstone and even limestone, have been found overlying or 

 underlying a bed of coal with no other strata intervening. 

 The rule mentioned is generally applicable to all coal-fields, 

 both in this country and elsewhere, but if one should expect 

 to find, farther than this, the same order of strata in different 

 coal-fields he will be mistaken, for they follow no more definite 

 order in this respect than the different strata of other forma- 

 tions do. To know the number and character of the beds of 

 coal in any coal-field, as well as of the different strata associ- 

 ated with them, one must study the region itself ; ior, with the 

 exception of obtaining a knowledge of some mere general 

 principles — and, by the way, many fail to obtain even this 

 before they are ready to offer their opinions for pay — all his 

 experience in other coal-fields will avail him nothing, 



We have found many persons holding the belief, that coal 



