MAPPING. 31 



area at about the width of one field apart ; if a pond, or 

 the chance of any other section offers, a divergence 

 thereto must be made. By walking over the ground in 

 this way, all the details of the strata, however numerous 

 they may be, are collected as it were at once, and a por- 

 tion, first of one line, then of another, is drawn, as we 

 cross and re-cross the boundaries. But sometimes it is 

 found more convenient to commence and follow out one 

 line this is best done by walking along a ditch or fence 

 until we cross the line, then along the bottom of the 

 field to the next fence, up this until the line is again 

 crossed, and so on. 



When walking over and geologically mapping any 

 area, it may seem almost impossible to, as it were, con- 

 vert oneself into a surveying machine to simply dig 

 out certain physical facts to put down on paper what 

 one actually sees or discovers, and for the time do no- 

 thing more yet this is the best plan that could be 

 adopted. The occupation itself affords much ground for 

 speculation, as to the extent of this rock, and the thick- 

 ness of that, the relation of the one to the other, the age 

 of each, and the amount of denudation to which it may 

 have been subjected. This is pleasant amusement enough, 

 and in one sense profitable also, but a geologist thus 

 reasoning in his own mind before he has obtained suffi- 

 cient data on which to base his ideas is really theorising ; 

 and it is astonishing to find how readily the facts 

 afterwards ascertained may seem to support a theory 

 thus pre-conceived. The machine-like method of pro- 

 cedure should be as far as possible followed, until a 

 considerable area has been accurately mapped, and all 

 available data obtained and correlated, then a theory, or 



