TK.\< I 



Neverthelcat, rach abrupt changes of contour, taken m 

 conjunction with other (act*, may often be made to help 

 in proving the existence of feulu. Marked forms of 

 ground have always some geological explanation. It 

 the province of the field-geologist to study them in con- 

 nection with their causes, and to make use of them in 

 elucidating the structure of the rocks and the history of 

 the physical geography of a country. 



Hut by far the most important and satisfactory evidence 

 for the existence and effects of faults is furnished by the 

 grouping of the rocks with reference to each other, and 

 can only be put together when that grouping has been 

 examined with some care, in other words, when some 

 progress has been made in unravelling the geological 

 structure of the locality. The nature of this evidence will 

 be most satisfactorily followed by reference once more 

 to the map in Figs. 27 and 28. 



It will be observed that several lines of fault are shown 

 upon that map. Look first at that which crosses the 

 streams on the left or west side (Z, Z). In ascending the 

 most westerly of these streams we notice that at first the 

 rocks consist of various sedimentary deposits sand- 

 stones, shales, and limestones. These strata dip toward 

 the south-east, and their angle of inclination gradually 

 rises as we proceed up the stream, until at the last place 

 where they are seen, they stand at an angle of 80*. A 

 short way higher up, we encounter rocks of an entirely 

 different character; let us suppose them to be granite 

 and crystalline metamorphic rocks (S, M). The gradual 

 rise of angle and the almost vertical position of the strata 

 would be regarded as sufficient to indicate the 



