﻿Vol. 64.] QUANTITATIVE METHODS TO THE STUDY OE EOCKS. 219 



ends. Taking, as visual, the shortest axis in the plane of bedding 

 as 100, the longest axis varies from 207 to 100 and the shortest 

 Irom 94 to 55, the means of all ray twenty specimens being 

 81 : 100 : 127. Those which are almost circular in the plane of 

 bedding, and therefore have a nearly-symmetrical nucleus, give for 

 the axes 79 : 100 : 10] : which differ from those in the case of the 

 large specimen by about a hundredth of an inch. Hence, at the 

 time when the concretions were formed, the relative permeability 

 of the rock in a line perpendicular to the stratification was about 

 79 per cent, of that in its plane. The prevailing greater length of 

 one axis in the plane of bedding was probably due to the nucleus 

 being more or less elongated, combined with a slight want of 

 symmetry in the rock, due to current. I have entered into all 

 these details, in order to show that the proper discussion of very 

 unpromising material yields nevertheless extremely satisfactory 

 and concordant results. 



Fortunately, I possess a few specimens of coarse shale with 

 included concretions. These show that the layers of the rock do 

 not pass through the concretions, but curve round them, as if the 

 shale had been compressed to about half its thickness since they 

 were formed, unless they (to some extent) pushed it aside in growing. 

 Of this there seems to be no good evidence, whereas experiment shows 

 that there must have been a great vertical contraction in shales and 

 clays. This is, however, a question which needs further investiga- 

 tions, differing from any that I have been able to carry out. 



The following (Table VII) is a list of all the concretions which I 

 have studied, with the ratios of their axes, the shortest axis in 

 the plane of bedding being taken as 100 : — 



Table VII. 



All axes nearly equal. 



1. Magnesian Limestone, Sunderland 100 100 100 



2. Post-Glacial, Bridlington 103 100 106 



Two axes nearly equal. 



3. In fine sand, Arborthorne 90 100 101 



4. Green spots, Old Red Sandstone 88 100 101 



5. Lower Coal- Measures, Stannington (small) 79 100 101 



6. Do. do. do. (large) 78 100 103 



7. Fisb-nodule, Old Red Sandstone 53 100 103 



8. Imperfect, Stannington 40 100 lOl 



Elongated nuclei. 



9. Post-Glacial, Bridlington 100 100 222 



10. Pyrites in Chalk 100 100 444 



All axes unequal. 



11. Gauit, Lidhurst 88 100 1.5.3 



12. Post-Glacial, Bridlington 86 100 136 



13. Lower Coal-Measures, Stannington 81 100 127 



14. Oxford Clay 77 100 143 



15. Coal-shale, Woodbourne .54 100 190 



Nos. 1, 3, 4, 5, 8, & 13 are means of a number of specimens, and 

 the rest single good cases. 



