114 MB. J. PARKINSON ON THE PXROAfERTDES [Feb. 1 898, 



The same brick-red colour is m an if est by incident light, the radial 

 structure present in both has the same characteristics, the black 

 microliths found in the one are seen in the other, the types of de- 

 polarization have many points in common. It is then interesting 

 to find that here, as in those cases from Boulay Bay where the 

 pyromerides are sufficiently small to enable their relations to the 

 surrounding matter to be certainly made out, the evidences of flow 

 as a factor of importance, which were described in the Jersey rocks, 

 are, as the diagram on the preceding page will show, also to be 

 found in connexion with the nodules from Shropshire. (See fig. 4.) 



The tongue-like ends which form part of the nodule and the 

 identity of its material with that of the flow-bands, the only dif- 

 ference being a certain amount of radial structure in the former, 

 appear significant. Also the concentric structure, which is but feebly 

 developed here and there, seems to show that it, like the radial 

 growth, was developed after the present form was assumed, rather 

 as a structure of secondary importance. 



From the preceding remarks it is apparent that many pyromerides 

 bear a relation to the enveloping rock similar to that which charac- 

 terizes those fragments of a lava-flow which have resulted from 

 flow-brecciation. They have distinguishing petrographical cha- 

 racters of their own, not identical with, often differing markedlj' 

 from, the surrounding materials ; they are connected with flow- 

 movement in the rock by gradation into such bands as are charac- 

 teristic of many lavas, and show occasionally contours which clearly 

 indicate that part of the diff'erentiated material was unable to 

 accommodate itself to the strictly spheroidal form of the more 

 perfect pyromerides. 



Turning from the form of the nodules to less evident structural 

 peculiarities, it has been seen that the radial structure is always 

 feebly developed, and that, in those cases ^ where a conspicuous in- 

 dentation of the edge occurs, the direction of growth is normal to it. 

 That such an appearance may be produced as a secondary structure 

 in a fragment the contours of which are by no means spherical 

 will be apparent from the following case. The rock from which the 

 slide was prepared forms the lower part of the crags abutting on 

 the more southerly side of the jetty at Boulay Bay. It is of the 

 chocolate-brown colour commonly found, and shows many elongated 

 fragments darker than the surrounding rock ; the latter in itself does 

 not differ materially from others in the neighbourhood, llie 

 fragments, which are sufficiently numerous to give both specimen 

 and slide rather the appearance of an ash, are rounded or angular, 

 similar to the lava which contains them, but still easily seen, more 

 especially as they are for the most part characterized by flow-hnes, 

 which of course terminate abruptly. Closer observation shows that 

 a radial structure has been set up, occasionally at one part only, 

 but sometimes irregularly all over : obviously secondary, as in other 



^ That is, the radial structure does not define the edge of the pyromeride, 

 but the edge of the pyromeride determines the direction of the radial growth. 



