142 COAL-FIELD OF CLACKMANNANSHIRE. 



and the inner elliptical line represents the crop or 

 outburst of the upper coal. Fig. 4. is the longitu- 

 dinal section of the line A B, and Fig. 5. the trans- 

 verse section of the line C D. All the accompany- 

 ing coal- strata partake of the same form and paral- 

 lelism. These basons are generally elliptical, some- 

 times nearly circular, but are often very eccentric, 

 being much greater in length than in breadth, and 

 frequently the one side of the bason upon the nar- 

 row diameter having a much greater dip than the 

 other; which circumstance throws the trough or 

 lower part of the bason much nearer to the one side 

 than to the other. From this view of an entire 

 bason-shape, it is evident, that the dip is in every 

 direction, and all the strata regularly crop out, and 

 meet the alluvial cover in every point. 



It is from this bason-shape that all the other coal- 

 fields are formed, which are portions or segments 

 of a bason produced by slips, dikes or dislocations 

 of the strata. If the coals Fig. 3. Plate IV. were 

 dislocated by two slips b c and d e, the slip b c 

 throwing the strata down to the east, and the slip 

 d e throwing them as much up in the same direc- 

 tion, the crops of the coals would be found in the 

 form represented in Fig. 6. ; of which Fig 7. is 

 the section in the line A B, and Fig. 8. the section 

 in the line C D. 



The chief difficulty which arises in exploring a 

 country in search of coal, or even where coal-fields 

 are known to exist, arises from the great thickness 



