SG OP BOUNDARY-LINES 



97 



rook the mailer itones in the soil, and permit 



an intVrmre to be drawn as to the probable nature of 

 the material* : decomposition of which the toil 



!ii. D6QB !:... I ' ' ' '..'.'.:. ! '.'..< 



rabbit lay bare not only the constitution of the soil, but 

 also the angular 4H . rests immediately 



upon the solid rock. 



From vegetation, also, the field -geologist learns to 

 draw many a shrewd inference as to the character of the 

 soil 'and rock below. ' t springs, indi- 



cative of some geological boundary - line, such as the 



r. i>-Setia of valley thovfa* OM 



t a harder or softer stratum , or a line 



of fracture ( l-'i^. ^7), will reveal itself by marshy ground 

 or by a brighter green along a hill slope. The course 

 of a limestone Kind or a basalt-dyke may be followed, 

 i)> the jt Jure of its vegetable covering, across 



a moorland where little or no solid rock may be seen. 

 e of serpentine stands up bare and rough, afford- 

 ing at best but an unkindly soil for plant-growth. Trees, 

 too, change with the varying character of the rocks or 

 soils on which they grow. Each country presents its 

 own illustrations of these relations, which must be gradu- 

 ally learnt and made to give their assistance to the 

 observer's progress. 



In judging of the probable character of the rocks 

 underneath from the nature of the overlying soil, the 



M 



