W. M. Hutchings — Rocks of Great Whin Sill. 69 



Waulsortian or Tournaisian in their faunas. My own view, from 

 a comparison of the Belgian and British fossils, is that the zone of 

 P. gtganteus in Great Britain and Ireland corresponds to the whole 

 of the Belgian series; for none of the fossils which are relied upon 

 by MM. Da Koninck and Lohest to identify the lower beds in 

 both areas are in Gi-eat Britain and Ireland confined to the Lower 

 Limestone Shales, but are found in abundance, and in a full condition 

 of growth, at the top of the zone of P. giganteus. 



The faunas contained in the beds of shale differ markedly from 

 those contained in limestones, the shales being much richer in 

 Lamellibranchs and Crustaceans, and comparatively poor in Brachio- 

 pods and the Actinozoa. Consequently the faunas of the same zone, 

 taken as a whole, vary very much according to locality and the 

 nature of the sediment. Consequently the zone of P. giganteus in 

 Scotland, in which the limestones are separated by thick beds of 

 shale, contains a very different fauna from that which obtains in the 

 same zone in Derbyshire, where the shales are practically absent, 

 and the limestone exists in one mass, made up of beds of various 

 litholoffical characters. 



IV. — The Contaot-Rocks of the Great Whin Sill. 

 By "W. Mayxaud Hutchings, F.G.S. 



IN what follows, it is proposed to give a general description of the 

 effects of contact-metamorphism, observed in the rocks altered 

 by the intrusion of the Great Whin Sill in Durham and Northum- 

 berland. 



The work, of which this is the condensed result, has been carried 

 on for the last four years in the microscopical, and to some extent 

 chemical, study of a large series of specimens collected at many 

 points along the course of the Whin Sill exposure by Mr. E. J. 

 Garwood, and also, to a very much smaller extent, by myself. 

 ]\Ir. Garwood has been for a long time engaged in a detailed 

 examination of the geology of the district, and will in due course 

 publish the results of his work, which is not yet complete. It was 

 at his suggestion and request that I undertook the petrological study 

 of the specimens collected. 



As is well known, the rocks into which the Whin Sill mass has 

 been intruded consist mainly of limestones, shales, and. sandstones 

 of the Lower Carboniferous beds. The special interest and value 

 of the contact-effects here displayed, are enhanced by the fact that 

 the rocks acted upon were all in what may be called a perfectly 

 simple and elementary state. We know exactly what they were 

 like before they were altered by the intrusion, and can study them 

 as fully as we wish, in their original and normal condition, in the 

 same and other districts. Thus, the shales, the metamorphism of 

 which gives us the most interesting portion of the material, with 

 the most important bearings vipou the question of contact-action in 

 general, are in all respects counterparts of those from the Coal- 

 measures and the Lower Carboniferous, which I have described in 



