L. C. Miall — On Contortion of Rocks. 



507 



angles have been deduced from the amount of perpendicular de- 

 flection, and they are consequently all taken as rectilinear. 



Experiments on Contortion of Mountain Limestone. 



No. 1. 



21b3. 

 Immediately 

 (broke at) 2-2° 



No. 2. ^1^ h 



21bs. 

 Immediately 

 (broke at) 2-5° 



7oz. 

 3 weeks 



7-4° 



7oz. 



3 weeks 



8-15^ 



No. 3. -j-i-p- (bituminous). 



21bs. 



Immediately 



(broke at) 275° 



7oz. 



3 weeks 



7-55^ 



No. 4. -j-|-^ (bituminous). 



21bs. 



Immediately 



(broke at) 2-15'' 



5oz. 

 3 weet 



7-r 



7oz. 



2 months 



11-5° 



7oz. 



2 months 



1015° 



7oz. 



2 months 



11-2° 



5oz. 



3 weeks 



12-5° 



Recovered in 



3 weeks 



2-7° 



Broke after 

 6 days 



Recovered in 



3 weeks 



31° 



Broke after 

 11 days 



Another circumstance connected with these experiments has some 

 interest in connection with geological phenomena. I have found re- 

 peatedly that the slabs, when bent to any considerable angle, have 

 exhibited a great tendency to break transversely. This has generally 

 appeared some days after the strain was removed. In those cases 

 where sharp, unbroken bends occur in rocks, the tendency to fracture 

 has been probably overcome by the pressure of superincumbent 

 mass. As yet I have not been able to imitate the natural conditions 

 so as to verify this explanation experimentally, but I have no doubt 

 of its correctness. In one well-marked instance in the Mountain 

 limestone district of Yorkshii-e an anticlinal flexure passes eastwards 

 into an anticlinal fault with gradually increasing displacement. The 

 geological evidence in this case shews unmistakably that the lime- 

 stone was covered at the time of disturbance by a considerable thick- 

 ness of upper Carboniferous strata, which are also known to have 

 materially diminished eastwards, — that is, in correspondence with 

 the alteration in the character of the anticlinal. 



Some interesting facts have been observed by the microscopic ex- 

 amination of the deflected substances, but these results require more 

 complete investigation. In order to operate upon thicker slabs, I 

 am preparing a micrometer screw which will read deflection to 

 1-1500 inch. At some future time I hope to bring a fuller collection 

 of observations under the notice of geolos-ists. 



