H. A. Baker — Loose Arenaceous Sedi'ments. 411 



S. infundihulum de Koninck. — Upper Beds of Dibunopliyllum 

 zone at Elbolton, Yorkshire ; Hollington End, Derbyshire. 



S. ingens Martin. — Upper beds of the Dibunophyllum zone. 

 Syn. Solenocheilus pentagonalis Phillips. 

 Little Limestone, Weardale, Durham ; Bradbourne and near 

 Ashford, Derbyshire 5 Astbury Old Quarry, Cheshire. Bathgate, 

 Linlithgowshire, Closeburn and Kirtlebridge, Dumfriesshire, and 

 Arden Quarry, Nitshill, Scotland. 



S. derhiensis Foord. — Upper Dibunophyllum zone. Park Hill, 

 Castleton, and Crowdecote, Derbyshire ; Narrowdale, Staffs ; 4 Laws 

 Limestone, Combe, Northumberland ; Poolvash, Isle of Man. I do 

 not consider the variety named S. derhiensis var. globularis of 

 Foord sufficiently distinct to be retained. 



S. glohosus Hind. — Millstone Grit, Lower Coal-measures. Caton ; 

 Sales Wheel, Eiver Ribble ; Bullion Coal, Carreheys, near Colne, 

 Burnley Coalfield, Lancashire ; the marine bed, Silica Quarry, 

 Congleton Edge, Cheshire. 



Cyclonautilus Hind. 

 Cyclonautilus umbilicatus Hind. — Coal-measures. Roof of the 

 Bullion Coal, Burnley. 



On the Investigation of the Mechanical Constitution 

 of Loose Arenaceous Sediments by the method of 

 Elutriation, with special reference to the Thanet 

 Beds of the Southern Side of the London Basin. 



By Herbert Arthur Baker, M.Sc, F.G.S. 

 [Continued from ij. 370.) 



Leading Characteristics of Elutriation-Curves op Sediments. 



TITITH regard to the laws governing the transport, sorting, and 

 ' ^ deposition of sediments, much has still to be learned, but one 

 fact emerges clearly from the mass of present data. During the process 

 of transport by water the load undergoes selective treatment, or, 

 in other words, is sorted. The late Dr. G. K. Gilbert, in the course 

 of his important work on the transportation of debris by running 

 water.^ carried out exjDeriments with mixtures of several grades of 

 detrital material and found that before the slope of the stream had 

 been definitely established (i.e. before the attainment of uniformity 

 of conditions), and especially when low velocities w^ere used, the 

 current tended to sort the debris, building deposits with the coarser 

 part and continuing to transport the finer material. This fact has 

 a special bearing on the study of natural sediments. The state of 

 equilibrium, or of perfect uniformity of conditions, is seldom, if ever, 

 completely realized in nature, and even when approximately reached 

 is not, as a rule, of long duration. Further, in general, the detrital 



^ Gilbert, " The Transportation of Debris by Running Water " : U.S. Geol. 

 Surv. Professional Paper 86, 1914. 



