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DE. H. C. SORBY OlS THE APPLICATION OF [May I908, 



Table VIII. 



Clay from an old lake at Sewerby ... 

 After Boulder- Clay, Bridlington ... 



Alluvial clay, Orgreave 



New Red Marl, Leamington 



3J 3> 35 33 •••; 



„ „ „ from a deep boring . 



33 53 33 33 JJ 35 



33 53 53 53 33 55 



Tertiary Clay, Watcli Point .'.'. '. 



„ Whiteclitr 



„ Barton Cliff 



Boulder- Clay, Bridlington 



53 55 55 



„ „ Balby (nr. Doncaster). 



_ 33 55 55 55 



Kimmeridge Clay, Oxford 



,5 Mley 



Xiassic clay, Batli 



J5 35 55 



„ „ Robin Hood's Bay ... 



49-5 

 lo•0'^ 



6-2 f ^"^ 



4-8 J 



28-4 }■ 28-8 



28-; 



25-5'^ 

 25-5 ^24-1 

 23-4J 

 24-1 1 

 23-9 3 

 30-7 ■ 

 19-0 

 27-71 

 23-0 ;-24-4 

 22'5J 



24-0 



24-8 



Gault, Aylesford 



„ Folkestone 



,, „ bottom 



Speeton Clay, weathered 



„ „ unweathered 



Coal-Meas. nr, Nottingham, 510 ft. . 



829 ft. . 



1190 ft. . 



„ Brightside 



„ Darnall 



Wenlock Shale, Malvern, weathered. 

 ,, „ unweathered. 



Slate, Mawnan (Cornwall) 



Slates, etc., Moffat, black 



28' 

 25 

 18' 

 18-4 



•0 ^24-0 

 •9J 



13-6 



13-41 

 14-6 j>12-9 

 10-7J 

 14-3 7 12.5 



55 red 

 55 green 

 Slate, Hele, Ilfracombe 



Westmorland slate, black 



„ „ Coniston 

 „ Langdale 

 Pui-ple slate, Peurhjoi 



12-8 

 14-1 



5-8 



5-9 



5-21 



3-8 I 



3-4 f 



2-lJ 



3-5) 



1-3 j 

 0-551 

 0-52 |>0-49 

 0-40J 

 0-24 



10-0 



3-6 



2-4 



A few remarks on these results may be apposite. The amount of 

 invisible cavities in the apparently-solid deposit from an old lake 

 at Sewerby is so unusual, that I thought I had made a mistake — 

 until I found that a second experiment gave exactly the same 

 result. The probable explanation is that the material is of ab- 

 normal character, and not comparable with clay. The percentage 

 of cavities in the jSlew Red Marl in some cases seems so abnormally 

 great as to indicate the removal by weathering of some constituent, 

 which is easily understood when we find that specimens from a 

 considerable depth in a deep boring, given to me by Mr. J. A. Howe, 

 contain so little of interspaces and also crystals of intercrystallized 

 calcite, giving fractures of uniform reflection. The amount of 

 cavities in a number of specimens of Boulder-Clay is so remarkably 

 uniform, as to make me think that this deposit deserves further study. 

 It is so much less than would agree v^ith the small pressure of the 

 material now lying over them, as to make me think that the clay 

 has been somewhat compressed by the lateral pressure which forced 

 it along, or by superincumbent ice, or by some other special cause 

 not fully understood. The great variation in the Gault and 

 Kimmeridge Clay is probably due to carbonate of lime. The much 

 smaller amount in the Speeton Clay than in the Gault , as in the 

 Yorkshire Chalk compared with that from many other localities, is 

 certainly due to this cause. The Liassic clays were fairly satisfactory. 

 Taking everything into consideration, the Coal-Measure shales give 

 good results. The specimens of Wenlock Shale at my disposal 

 were unsatisfactory, since one contains too much carbonate of lime, 

 and the other is too much weathered. The variations in the slaty 

 rocks of Mawnan, Moffat, and Hele are in some cases most certainly 

 due to varying pressure connected with slaty cleavage. What is 



