TRANSACTIONS OF THE SECTIONS. 65 



Notes on the Variations in CJiamctei- and TJiicJcness of the MiUstone-fjrit of 

 North Derbyshire and the adjoininci parts of Yorkshire, and on the prohahle 

 manner in which these Changes have been produced. By A. H. Gkeen, 

 3LA., F.G.S, 



The Millstone-grit of tlie district treated of was subdivided as follows : — 



Top. 

 (3) Eoug-h Eock, 

 i2\ Middle Grits. 

 (1) Kinder-Scout Grits. 

 Jiottom. 



^ (3) is a bed whicL, in spite of some local variations, may be fairly spoken of as 

 singularly constant in cbaracter and thickness. 



(2) is a remarkably changeable group. In Derbyshire its most striking member 

 is the Grit of Chatsworth (the Third Grit of the Geological Survey) ; this was 

 shown to be a bed of only local occurrence, thinning away and disappearing entirely 

 to the north. The beds above the Chatsworth Grit in Derbyshire which are called 

 Second Grits by the Geological Survey, and the rocks in South Yorkshire which 

 are called Third Grits by the Geological Survey, were shown to be in a general 

 way the equivalents of one another, though, on account of the numerous changes 

 that are met with in passing from place to place, no correlation of individual beds 

 was possible. 



(1) is a group less changeable as a whole than the Middle Grits, but liable to 

 many local variations. One very striking case of the sudden thinning away of a 

 great mass of Grit and Conglomerate that forms its base in Derbyshire was de- 

 scribed. To account for the variations spoken of, it was pointed out that wedge- 

 shaped masses of sandstone have been, sometimes banks formed in shallow water 

 and tailing out in the direction in which the water deepened, sometimes heaps piled 

 up by the action of opposing currents. But it seemed that in the present case the 

 occurrence of lenticular masses of sandstone could in several instances be best 

 explained by supposing that the floor on which these beds were deposited was very 

 uneven and full of hollows, and that the great cakes of sandstone had been formed 

 by the filling-up of these depressions Iby drifted sandy sediment. 



Notes on Carboniferous Encrinites from Clifton and from Lancashire. 

 By J. G. GuENFELt, B.A., F.G.S. 



The author exhibited and described a series of Poteriocrinm plicatus from the 

 base of the Carboniferous limestone in the gorge of the Avon. The new facts 

 brought to light by these specimens are the anal plates, the arms which bifurcate 

 four times, giving eighty rays, the stem and its side arms, and a very remarkable 

 proboscis exhibiting a structure hitherto unknown amongst the Crinoids. One of 

 these is 4^ inches long by f inch wide, and is composed of long narrow plates 

 ai-ranged m five horizontal rows with longitudinal and transverse rido-es. 



The total number of plates is upwards of 1.300. ° 



A new species of Poteriocrinus was then described, P. rugosus (GrenfeU), found 

 in the Lower Limestone Shales, Clifton, which resembles P. pentagoiws and 

 P. lomjidactijlus (Austin), but is distinguished by the depression of the ano-les and 

 lateral articulations of the body-plates, and by the surface of the body being rouo-h 

 and that of the arms strongly wi-inkled. ° 



A specimen of Rhodocrimis venis from Clifton showed that the rays of this species 

 hitherto unk-nown, were twenty in number and closely tentaculated. Miller's 

 figures of this species include a distinct Silurian fossil, for which Phillips and 

 De Koninck would retain the name P. vents. Since, however, Miller's detailed 

 drawing of the species agrees with the specimen exhibited, it was urged that this 

 latter has the best claim to the name. 



Jthodocrinui verisimilis (Grenfell), a new species from Olifton, was described. It 



