

ECONOMIC ASPECTS OF GEOLOGICAL STRUCTURE 335 
out as they are followed downwards. But if the strata are 
undulating and the same beds come again and again to the 
surface—each recurring coal-seam continuing thin and unim- 
portant—he will have good reason to infer that the series is 
not worth further investigation. Should the rocks, however, 
be partially concealed by overlaps or unconformities or by 
faulting, or otherwise not be accessible, owing, perhaps, to 
thick coverings of surface accumulations or to the paucity of 
sections, the observer would not be wise to abandon his 
search. The occurrence of thin seams of coal, or even the 
mere presence of numerous plant-remains such as are 
commonly associated with coal-bearing strata, taken in con- 
nection with the obviously shallow-water origin of the strata 
and the absence of any evidence of deep-sea or purely marine 
conditions, would be sufficient to justify trial-boring. The 
frequent occurrence of rootlet-beds, with or without over- 
lying coal-seams, would suggest the probability that the 
unexplored parts of the series might contain more or less 
persistent beds of coal. The absence of rootlet-beds, however, 
would not be quite so favourable a sign. It would lead to the 
inference that any workable coal-seams that might occur would 
be apt to be somewhat inconstant—lenticular sheets, thickening 
and thinning irregularly. But, inasmuch as seams of this 
character not infrequently attain a very considerable thickness 
and extend over wide areas, it would obviously be important 
to ascertain the direction in which thickening was likely to 
take place, and thereafter to test the ground by borings. 
The Search for Ore-Formations.—Bedded ores occur 
under the same conditions as any other sedimentary rock, and 
are therefore to be sought for and traced by the ordinary 
methods employed in field geology. The same to a large 
extent is true of lodes and irregular ore-formations of all 
kids, but the search for these is not, as.a rule, so easy. 
Perhaps most discoveries of such ore-deposits have been the 
result of accident. A large number, however, must be credited 
to those sanguine and often admirable observers, known as 
“ prospectors,” the most successful of whom have, wittingly or 
unwittingly, usually followed geological methods of research. 
Having become familiar with the ore-formations of some 
particular region, and learned to recognise the manifold 
