98 SECTION AT ONE TREE POINT, 



K.S. TAS. 



particularly his Fig. 2, the section opposite Sandy Bay 

 Point, offer a most serious objection to his own hypothesis; 

 leastways they are capable of quite a different interpreta- 

 tion. As shown by bim in Figure 2, the leaf beds abutting 

 against the Palaeozoic rocks are bent upwards. Now, such an 

 effect will never be produced during sedimentation ; only 

 a subsequent downward movement of the strata can pro- 

 duce such an eft'ect. Mr. R. M. Johnstons Figure 2 

 plainly suggests the existence of a trough fault ; that is to 

 say, that the leaf beds were deposited at a much higher 

 level than they are now, and that subsequently the whole 

 mass moved downwards along two great faults, one of 

 which is running approximately parallel to the Mount 

 Nelson range, and that during this downwai'd movement 

 it was broken, the different pieces acquiring the southern 

 tilt. Of course, if it can be proved that the leaf bed series 

 are preserved in a trough fault, the "lake" hypothesis, not- 

 withstanding its seductiveness, has to be abandoned. Before 

 we decide we will have to make further investigations, and 

 I refrain from expressing my opinion one way or other; 

 for the purposes of this paper I accept Mr. Johnston's lake 

 hypothesis, because the main results will not be affected 

 by it. Should, however, future investigations prove that 

 the leaf bed series rest now inside a trough fault, many 

 of the seemingly incongruous features would easily explain 

 themselves. 



Mr. B. M. Johnston has already noticed that the leaf 

 bed series have a very unifoi'm dip towards south, and are 

 traversed by a series of faults, which run apparently nearly 

 parallel in north-west, south-eastern direction. These 

 faults have produced a feature known as step faults ; thafc 

 is to say, while one- end of the mass of rock remained 

 stationary, the other moved downwards. In the leaf bed 

 series apparently the southern end of the mass between 

 two faults moved downwards, while the northern end re- 

 mained stationary. I may point out that this is a feature 

 frequently obsein^ed in strata preserved in trough faults; 

 for instance, in the coal basins of Giridih, in Bene^al. 



3. Description of the Section at One Tree Point, 



The sequence of the strata as seen in the above sectioii 

 is as follows (see Plate iv.) : — 



(a) Northern part. 



(5) Vesicular Basalt, about 18 feet. 



