Notices of Memoirs — W. WJiitaker — Deep Borings at Chatham. 561 



Bettish Association : Aberdeen. 



Papers read before Section C. Geology. 



I. — On Slaty Cleavage and Allied Rock-Structures ; with 



SPECIAL EePERENCE TO THE MeOHANICAL THEORIES OF THEIR 



Origin. By Alfred Harker, M.A., F.G.S. 



SINCE Professor Phillips' Report to this Association in 1856, the 

 subject of Cleavage, especially in connection with Foliation, 

 has received much attention. In the present communication the 

 mechanical theories of Mr. Sharpe and Dr. Sorby are discussed at 

 length, and pursued through their various consequences, such as the 

 variation of Cleavage in rocks of different natures and the peculiari- 

 ties of Cleavage-planes which traverse alternating strata. A section 

 is devoted to the mode of working slate-rock in the quarries, which 

 throws much light on the structure of the rock. The spurious and 

 incipient Cleavages due to minute contortion or faulting of the rocks 

 are next described. A consideration of the general effects, mechani- 

 cal, physical, and chemical, of pressure upon rocks leads to a discus- 

 sion of the relations between Cleavage and Foliation, and the extent 

 to which the latter can in many cases be referred to the action of 

 mechanical forces. The concluding section deals briefly with the 

 relation of Cleavage to Earth movements. 



II. — On Deep Borings at Chatham. A Contribution to the 

 Deep-seated Geology of the London Basin. 



By W. Whitaker, B.A., F.G.S., Assoc.Inst.C.E. 



A FEW years ago the Admiralty made a boring in the Chatham 

 Dockyard extension, to the depth of 903| feet, just reaching the 

 Lower Greensand, and in 1883-4 followed this by another boring, 

 near by, to increase the supply, which has led to an unexpected 

 result. After passing through 27 feet of Alluvium and Tertiary 

 beds, 682 of Chalk, and 193 of Gault, the Lower Greensand was 

 again reached ; but, on continuing the boring, was found to be 

 only 41 feet thick, when it was succeeded by a stiff clay, which, 

 from its fossils, is found to be Oxford Cla^^ a formation not before 

 known to occur in Kent. 



At its outcrop, about seven miles to the south, the Lower Green- 

 sand is 200 feet thick, and is succeeded, a little further south, by the 

 Weald Clay, there 600 feet thick. Not only, however, has this 

 600 feet of clay wholly disappeared, but also the whole of the next 

 underlying set of deposits, the Hastings Beds, which crop out every- 

 where from beneath the Weald Clay, and are also some hundreds of 

 feet thick. 



More than this, the Purbeck Beds, which underlie the Hastings 

 Beds near Battle, are absent, and also the Portlandian, Kimmeride:e 



DECADE III. — YOL. II. — NO. XII. 36 



