334 Correspondence — Mr. E. J. Garicood. 



in coal-seams. During their deposition very numerous eruptions of 

 felsite-porphyry, melaphyre, palatinite, and porpliyrite occurred, 

 and formed dykes, intrusive layers, and tabular lava-flows (platten- 

 farmige Effusionsschicliten) between the sedimentary rocks" (p. 516). 

 Further details of the stratigraphy are also given {Inc. cit.). 



I am glad to find my contention in the paper wlaich appeared last 

 February (Q.J.G.S.) supported by the establishment by Professor 

 Bucking of the lithological identity of some of those rocks with 

 igneous rocks of the Devon Permian ; although, as an argument 

 based on the assumption of a strict temporal order of succession 

 among igneous rocks, it has not much weighed with me. I must 

 remind Mi\ Ussher that those, who know how the basis of our 

 classification of the Midland Permian and Trias was laid for us by 

 the labours of Prof. Hull in former years, can hardly be expected to 

 admit his statement on p. 249, that "the Midland sections owe their 

 importance as a basis for correlation entirely to the merits of the 

 assumed correctness of their classification with reference to the 

 German types." The fact that the Devon and Midland areas were 

 at the time disconnected does not affect the question, as a careful 

 study of my papers, and that of Prof. Hull (1892), will make clear 

 to any candid mind ; papers based on observations by no means 

 limited to the coast-section. 



Wellington College, Berks. A. IkvinG. 



Uth June, 1892, 



CONE-IN-CONE STRUCTURE. 



Sir, — Mr. Young's statement that " The apices are invariably 

 turned to the under or lower side of the structui-e while their bases 

 are as invariably directed to the upper surface," ^ is certainly not of 

 universal application. In addition to examples instanced by Mr. 

 Harker,- from the Lingula Flags and Lias shales, I may mention, 

 specimens of my own of concretions from the pencil slates in Swin- 

 dale and from Carboniferous shale in Northumberland, which exhibit 

 a similar radial arrangement of the cones. But the beds which 

 afford the most striking refutation of Mr. Young's statement are the 

 Coal seams, for it is in these beds that the structure is by far the 

 most extensively developed portions of some seams several inches in 

 thickness being made up of these cones. Examination of numerous 

 specimens from the coal fields of Durham and South Wales show 

 two systems of arrangement of the cones — one, where the cones 

 have formed at right angles to certain laminae of deposition and 

 on hath sides of such laminae which are |— 1 inch in thickness, so 

 that the apices of the cones above point downwards, whilst those 

 below point upwards, both sets of cones having evidently formed 

 outwards from the same set of laminae. But the commonest dis- 

 position of the cones, especially in the Durham seams, is parallel to 

 the bedding planes, and although the apices often run for some 

 distance pointing in a constant direction, cases are of frequent occur- 

 rence where the bases of the cones start back, the apices being 

 directed away from each other. 



1 Geol. Mag. for March, 1892, p. 138. * Op. cit. May, 1892, p. 240. 



