
332 STRUCTURAL AND FIELD GEOLOGY 
engineer has encountered a _ succession of strata closely 
resembling those which in other parts of the world have 
yielded coal-seams. He naturally examines carefully every 
rock-section in the hope of discovering outcrops of the fossil 
fuel. This hope, however, might not be realised, for, owing 
to weathering, sections are often rendered more or less 
obscure, and outcrops of readily yielding beds are frequently — 
concealed under sheets of débris. Search in the alluvial 
deposits of the valleys, however, might be rewarded by the 
discovery of fragments of coal, and the source of these would 
be tracked up-stream in the usual way (see p. 289). Were 
the region not thickly covered with superficial accumulations, 
outcrops of coal might be expected to betray their presence 
by the blackened soils and subsoils resting upon them. 
Having satisfied himself as to the presence of coal, the 
engineer would proceed to open up any outcrop, so as to 
ascertain the thickness and quality of the seam, and the 
nature of the “roof” and “floor:’ Should the coal Msemaas 
thin or too poor in quality to pay the cost of working, we 
should not necessarily give up all hope. The engineer would 
probably suggest that before abandoning the search the 
ground should be proved by putting down one or more 
bore-holes. Before any such attempt is made, however, the 
geological structure of the area ought to be worked out, the 
character of the strata most carefully noted, and some reason- 
ably clear notion formed as to the conditions under which 
the strata have been accumulated. It may be that the coals 
are persistent at definite horizons throughout the whole area, 
or, on the other hand, they may be merely lenticular seams 
of no great extent, and occurring at irregular intervals, In 
the former case, it is obvious that a valuable coal-field would 
be waiting development, while in the latter case the chances 
of striking a workable seam: might be too uncertain to attract 
the attention of capitalists. 
Careful investigation of the exposed sections should 
enable the observer to decide the question. If he be a 
geologist he will know that coal has been formed in two ways: 
sometimes it represents swampy accumulations—the accumu- 
lated growth of plants zz sztu—at other times it would appear 
to consist of drifted vegetable débris. In either case the fossil 

