Charles Davison — Work done by Lobworms. 489 



silty clay when dry rubs on to the fingers like flour. This peculiar 

 constitution, together with the fine sandy laminations at which the 

 cla}' readily separated, rendered the material very " short" on drying, 

 facilitating its rupture by shearing and the keying up of its divided 

 portion by wedging, on the principle known to mechanics as " fox 

 wedging." If the bands were replaced in their original position, 

 they would not fill up the gap. The material must shrink a good 

 deal in drying. 



If we substitute volumetrical-contraction by change of temperature 

 for contraction by loss of moisture, and increase the size, weight, 

 and rigidity of the beds, we have at once my theory of Normal 

 Faulting, as explained in chapter viii. of the Origin of Mountain 

 Ranges. It is certainly remarkable how the material gets repacked 

 by shearing and wedging up, even in such miniature faultings as are 

 here described. There are absolutely no cavities, the faults being 

 mere lines, so close do the constituent pai'ts fit each other. No doubt 

 Nature reproduces great faulting in this miniature manner through 

 the small shearing strength of the beds. Had there been more clay 

 in the material, it would have proved too plastic for the purpose. 

 In the actual faulting of the earth's crust the weight of the rock is 

 much greater in proportion to the shearing stress brought into play 

 by contraction. 



In conclusion I ask, as a suggestion for the consideration of those 

 who have studied the subject, whether the minute faults sometimes 

 found in banded slates have not been produced in somewhat the 

 same manner.^ It certainly seems clear to me that the faulting in 

 such cases has preceded the cleavage. 



IV. — On the Amount of Sand brought up by Lobworms to the 



Surface. 



By Charles Davison, M.A., 

 Mathematical Master at King Edward's High School, Birmingham. 



TEN years ago Charles Darwin published his last work,^ the 

 result of more than forty years' observations on the habits of 

 earthworms and the rate at which they bring up soil to the surface. 

 To ascertain this rate, he made use of two methods. In the first 

 place he measured the rate at which layers of lime or cinders were 

 covered over by the spread-out castings of worms ; and, later, he 

 collected and weighed all the castings thrown up over a definite 

 area within a given time. As is well known, the general result 

 of his investigation was greatly to exalt our ideas of the importance 

 of earthworms and of the work they do upon the surface of the land. 

 The work performed by lobworms on the surface of tidal sands 

 seeming not less worthy of study, I made some observations on the 

 subject during a short stay in Holy Island last August. Between 

 this island and the opposite coast of Northumberland is an expanse 



1 See " A Faulted Slate" by J. J". Harris Teall, Geol. Mag. 1884, pp. 1, 2. 

 '^ "The Formation of Vegetable Mould, through the action of Worms, with 

 Observations on their Habits," 1881, 



