Trof. J. F. Blake — Recent Papers on Faults. 



367 



cause. The succeeding remarks, however, may be intended to prove 

 that it is so, though it is very obvious they do not. In the first 

 place, faults are essentially differential phenomena, and cannot be 

 brought about by anything which affects the stratum as a whole. 

 This may be seen in his Fig. 7; for if the pieces at the side were 

 equally contracted, the gaps would be filled up and there would be 

 no fault. Nothing is said about unequal contraction, so no reason is 



" B." series, 



Main Fault. 



"B." series. 



: "A." series. 



Diagram of Mr. Teall's Faulted Slate (see Geol. Mag. Jan. Ao. PL I. p. 1, 1884.) 



given why one part should contract more than another. This con- 

 traction theory is sometimes given for joints, of which it is a possible 

 account in some instances ; but the result of attempting to form 

 faults this way may be seen by the remarkable Figures 8 and 9. In 

 the first of these we have two faults crossing without dislocation of 

 either ! in spite of the correct relations having been given in Fig. 3. 

 In the second we have a kind of mosaic of such errors, and finally 

 faults dying out against an overlying stratum " which does not con- 

 tract," and which was therefore supposed to be there when the 

 faulting took place. Does any geologist know such faults ? If not, 

 it is of no use wasting time in trying to conceive how the bits in 

 Fig. 9 were arranged before they all contracted. Certainly none 

 such occur on Mr. Teall's slate. Here, however, we come to the end 

 of this theory of faults. Is it proved ? What has been done towards 



