360 



A. C. LAXE WEIGHT OF SEDIMENTARY ROCKS 



Porosity, 

 per cent. 

 (He calls attention to this as approached by many sandstones and 



as furnishing a more rapid flow in one direction, which is, of course, 



true in most natural sediments.) 



4. Tetrahedral packing (no greater velocity in one direction than an- 



other) , one sphere rests on three 25 . 95 



B. Spheres unequal Size 



5. Eight spheres on cube corners, size (a), one at center between them 



(size, a v / 3 — 1) (equal flow in three directions) 27 . 121 



6. Tetrahedral packing as in group 4, with small spheres at center of 



tetrahendron ( .2245 a = a ( t 6 — 1 / 2) , equal flow 24 . 28 



7. Tetrahedral packing as in group 4, with small spheres whose cen- 



ters are at center of tetrahedral faces, whose radii are .414 a = a 



(]/2 — 1) 20.67 



8. Tetrahedral packing with both kinds of small spheres of 7 and 8 . . 19 . 02 



Of course, in nature this perfect condition is not reached, but in gen- 

 eral it may be said that irregularity of shape will increase the porosity, 

 and irregularity in size will generally decrease it, though it may not if 

 the proportions of the smaller grains are too near those of the larger. 



We see that the range of the theoretical figures is quite that of the 

 practical figures given by Trautwine. 



We summarize Moore's 129 tests, beginning with the lightest: 



Gm 



Pumice 2 . 25 



Cave earth (Kent's tavern, Torquay) . . 2.67 



Friable I^ocene sandstone 2 . 61 



Red Triassic "bunter"' sandstone, about 



like Boston brownstone, highest 2.62 



Average of seven not indurated pieces. 2.63 



Hard layer 2.62 



Layer condensed by fault 2 . 62 



Permian Penrith sandstone 2.64 



Average of tests on Permian and Trias 2.63 



Millstone grit, coarse 2 . 63 



Millstone grit, fine 2 . 64 



Devonian Upper "Old lied" 2.59 



Cambrian Olenellus sandstone 2.61 



African auriferous quartzite 2 . 66 



Conglomerate and pebble beds do not 

 differ much from sandstones, though 

 with a less maximum. 





Weight in tons per 

 cubic meter. 



A 



Porosity. 



Wet. 





Dry. 



J64.1 



.... 





.... 



^63.63 

 21.23 



.... 





.... 



.... 





.... 



33.8 



2.18 





1.86 



30.80 









28.21 



2.13 





1.85 



13.18 



. . . . 





• • • • 



11.18 



. . . . 





• • • • 



24.80 



• • . . 





• • • • 



20.61 



2.27 





2.07 



18.20 



.... 





• • • • 



13.01 



.... 





• • • • 



15.95 



.... 





• • • • 



6.13 



.... 





• ■ • * 



1.91 



.... 







