Ruskin — On Banded and Brecciated Concretions, 159 



diametrically crossing their beds. On the other hand, true reniform 

 structure is perfectly compact, and dependent on minute radiating 

 crystallization of substance. But between the two there is the fine 

 agatescent structure, in which bands of different materials, jasperine 

 and chalcedonic, are separated from each other under a radiating 

 law ; and yet not divided by a mechanical contraction ; for though 

 they are often so distinct as to separate under the hammer stroke, 

 they never leave spaces between, as true pisolitic beds do in ultimate 

 separation. For this intermediate action, the most frequent of all, 

 I shall keep the term " spheric ;" and I was forced to admit only a 

 guarded use of the word '' gravity" in last paper, because this spheric 

 action is constant, as far as I know, in all agatescent matter, so that 

 I have never yet seen an instance in level-laid agate of the transition 

 from the lake in the (lowest ?) part of the cavity to the beds at the 

 sides being made under any subjection to the mechanical law of 

 gravity on fluent substance ; but (as in the petrifaction of the banks 

 of Dante's Phlegethon lo fondo suo, e amho le pendici, fatt 'eran pietra, 

 e i margini dal lato, '' its bottom, and both the slopes of its sides, and 

 the margins at the sides, were petrified"), the flinty bands form in 

 parallelism on the slopes as well as the bottom, and retain this parallel- 

 ism undisturbed round the walls and vault of the agate. On the other 

 hand, I cannot but admit the idea that these rectilinear tracts are 

 formed under a modified influence of gravity, because, first, I have 

 never seen them laid in difi'erent directions in different parts of the 

 same stone ; and, secondly, whenever they are associated with pendent 

 stalactites, they are at right angles to them. So that the aspect of 

 one of these levelled agates in cavities may be approximately de- 

 scribed as that of a polygonal crystal in which the position of one of 

 its sides is determined by gravity ; and the other sides modified into 

 curves by radiating crystallization (of course the changes of form 

 caused by gradual entrance or exit of material being at present with- 

 drawn from consideration). In the example before us, which, 

 though showing but feeble crystalline energy, belongs to the stellate 

 group, the outer formation of rudely spheric white jasper withdraws 

 itself confusedly from the sandy crust of quartz and becomes finer 

 and finer towards the inner jasper, on the surface of which it throws 

 down a coating of superb crimson (oxide of iron ?) which is itself 

 arranged every here and there in minute spherical concretions. The 

 same formation exists in the same position under the quartzose outer 

 bed and on the surface of the chalcedonic interior one, in the speci- 

 men figured in Plate III. Pig. 3 ; and when we find it, as we often 

 shall in future, under similar circumstances, I shall speak of it 

 simply as the " medial oxide." In the map, this crimson deposit is 

 throughout represented as black. 



Proceeding next to examine the inner formation on the surface of 

 which this medial oxide is deposited, we find it composed of two 

 parts, sharply divided ; a white jasper, and dark grey translucent 

 chalcedony. The white jasper has a spheric structure much more 

 perfect than that of the outer coat, and so delicate as to be hardly 

 visible without a lens (not that the spheres are small, — they are on 



