﻿218 DE. H. C. SOEBY ON THE APPLICATION OF [J^^J I908, 



diameter, which can easily be measured to a hundredth of an inch. 

 The material is of fine grain, the particles varying in size from 

 a hundredth of an inch down to very small. It is very compact, 

 and by the boiling-water method was found to contain only 

 7*2 per cent, of cavities. There is no indication of a bottom- 

 current of as much as 6 inches per second ; and the whole structure 

 is that of a deposit formed in fairly-deep water, the chief current 

 being some distance from the bottom. In the plane of symmetry 

 the ratios of the axes are 100 : 101, the variations from this 

 being only a hundredth of an inch. Perpendicular to the plane 

 of symmetry the axes are 88 : 100, or closely the same as in 

 the concretions at Arborfchorue. Unlike them, they cannot be 

 obtained separate, and are merely the red colour discharged by the 

 deoxidizing action of some nucleus. It is important to observe 

 that the plane of symmetry in all my specimens is inclined at about 

 10° to the stratification, probably because the bottom was not 

 horizontal. 



A small concretion from the Coal-Measures at Woodbourne (near 

 Sheffield) is an excellent illustration of the laws of formation. It is 

 split open through the centre, showing the exact shape of the nucleus, 

 which is very much like the seed of a plant. The dimensions of this 

 are : perpendicular to the plane of symmetry '2 inch, and in the pla'fie 

 •33 and '50. In this plane the deposit is on two sides -55, and on 

 the other two '60 ; so that, including the nucleus, we have for the 

 entire concretion -33 + 2 x 55 = 1*43 and -50 -|- 2 x 60 = 1*70. Hence 

 there is not equality, but rather more deposit in the line of the long 

 axis of the nucleus, jDrobably due to a slight difference in structure 

 in the direction of the gentle current, which caused the long axis of 

 the nucleus to lie in that direction. Perpendicular to the plane of 

 symmetry, we have for the shortest axis '20 -|- 2 x '28 = "76; so that 

 the three axes are -76, 1*43, and 1*70. It is also important to 

 notice that the plane of approximate symmetry is inclined to the 

 stratification at an angle of 5° in the line of the longest axis of both 

 nucleus and concretion, as though the bottom dipped in the line of 

 current. 



In the case of a concretion from the Coal-!Measures at Broomfield 

 (Sheffield), in a fine-grained sandstone, the plane of symmetry 

 appeared to be inclined at about 20° to the stratification, which may 

 be partly due to compression near a fault. 



In driving a drift through the Lower Coal-Measures at Stannington 

 (near Sheffield), some very large and perfect concretions were found 

 in a sandy shale. One of these, over 7 inches in diameter, gives as 

 the ratio of the axes 78 : 100 : 103. Besides this, I collected a con- 

 siderable number of much smaller size, down to less than an inch 

 in diameter. The variation in their shape is so great, that at first 

 sight it might seem impossible to deduce from them any general 

 conclusions. A few differ completely from the rest, being broad and 

 flat, imperfectly consolidated, and break up in the plane of bedding. 

 In my specimens the ratios of the axes are closely the same as 

 40 : 100 : 101. By far the greater number are, however, hard and 

 solid, but vary in general shape, one tapering off to a point at both 



