
AEE EINIOIOS B 
THE, SCALE OF HARDNESS 
BR Tale 6. Orthoclase. 
2. Rock-salt or Gypsum. 7. Quartz. 
3. Calcite. 8. Topaz. 
4. Fluor-spar. g. Corundum. 
5. Apatite. 10. Diamond. 
bee NOLX C 
TRUE AND APPARENT DIP 
In the late Professor A. H. Green’s admirable Physical Geology the 
student will find a full statement of the methods employed for ascertain- 
ing the amount and direction of the true dip from measurements of the 
apparent dip exposed in two sections making a large angle with one 
another. The student may usefully consult also Mr Penning’s field 
Geology, and the same author’s Azgineering Geology, on the same 
subject. A little experience, however, will soon convince the observer 
that the accuracy of an isolated dip obtained in this way can only be 
relied upon for the particular spot at which it is taken. Unless it be 
confirmed by more or less numerous observations in the neighbourhood, 
the precise direction and amount of the dip calculated from two or 
more apparent dips may not have much significance. We judge so from 
the fact that in regions where outcrops are abundantly exposed, the 
direction and angle of dip often vary within short distances. Not much 
reliance, therefore, can be placed upon an isolated dip, no matter how 
carefully its direction and angle have been calculated. The probabilities, 
however, are that the field geologist will seldom or never have occasion 
to use any of the methods or formulz referred to. 
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