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SPHERODIAL STRUCTURE IN SILURIAN ROCKS. 

 By the Rev. J. D. LA TOUCHE. 



It will hardly be necessary to remind those who have studied the Silurian 

 strata that spheroidal masses are met with in them of almost every size, some- 

 times deejily imbedded in the stone, at others, an entire mass of rook is arranged 

 with reference to a spherical contour. Sometimes the imbedded nodule is a hard 

 calcareous kernel ; at others, especially where it is of great size, it differs but 

 little from the surrounding rock. 



It may be desirable to specify these varieties of structure more accurately. 



The AVenlock shale affords a very marked example of it. In this forma- 

 tion, either a multitude of smaller nodules are found irregularly dispersed 

 throughout, or, as at "Wenlock Edge and elsewhere, long lines of them are 

 arranged with the regularity of bricks in a waU. 



These nodules are more or less calcareous. They give the impression of 

 an original \iniform deposit of limestone having been broken up or rather 

 rearranged in that form. That fossils have determined their position may be 

 doubted from their gi-eat regularity and because it is rare to find any trace of 

 organic remains in them. 



We must not omit to observe here, those remarkable accretions of lime- 

 stone found at 'Wenlock Edge, Dudley, and elsewhere, locally called ball-stones, 

 ■which are so extensively used for the iron works of the neighbourhood. They 

 vary in size from a few feet to some hundreds of yards, and are, for the most 

 part, of irregular shape. Sometimes, in process of formation, they have evidently 

 caused a distui'bance or dislocation of the adjacent rock. In all instances that 

 I have had occasion to examine them, tliis has been the case. They generally 

 extend too far below the exposed surface to enable the underlying strata to be 

 seen, but the overlying rock is invariably arched and iiushed up out of its 

 natural position by them, and where it can be examined, the subjacent rock 

 is found to be so also. In many cases the rock on each side of them is seen to 

 enter the mass of ball-stone and its stratification to be, as it were, lost in it. 



In the above instances the nodule consists of a different kind of stone to 

 its matrix, having, for the most jjart, a high per centage of lime. In the 

 examples which follow, such is not so strikingly the case, although there is no 

 marked line of demarcation between the two kinds of structure. 



I have before me a piece of lower Caradoc sandstone, a few inches square. 

 The central part consists of a bluish grey micaceous and somewhat argillaceous 

 sandstone, of an oMong rounded shape, and around it are three rings of alter- 

 nately yellow and blue coloured sandstone; apparently the yellow bands are 



