TRANSACtlONS Of SECTION C. 703 



Upper beds of mountain limestone, associated with chert, and in some beds of 

 white mountain limestone. These rocks have little definite structure under the 

 microscope. In some cases, especially in the limestone shales, they contain sponge 

 spicules. 



Some of the massive white limestones have a micro-granular or micro-oolitic 

 structure, like the limestones above the upper lava flow of Millers Dale. The 

 granules consist of pellets and small oolitic grains with minute fragments of 

 organisms. 



Many limestones, both black and white, are composed mainly of foraminifera, 

 with or without minute shell fragments, often enclo'ed in a calcite cement. 

 (Foraminifera are present in most of the specimens examined.) 



The coarse-grained limestones consist of granular and shelly limestones. The 

 granular type includes the oolitic and the pebbly. One or both of these may be 

 present in the same thin slice. The oolitic grains often ha\e a nucleus of a fossil 

 fragment. The pebbles consi&t of previously consolidated limestone, with fossil 

 contents, and are evidently detrital. The granular structure is found at various 

 horizons, and in many parts of the mountain limestone district. It frequently 

 occurs above a bed of clay or of volcanic tuff, and has probably been formed in 

 shallow water. The interspaces between the pebbles, oolitic grains and fossil 

 fragments form about 25 per cent, of the whole rock. They are composed of 

 crystalline calcite, and, according to Dr. Sorby's experiments, the rock has been 

 subjected to considerable pressure previously to the infiltration of calcite. The 

 shelly limestones contain fragments of brachiopods and productus which are 

 waterworn. In some rocks there is a more or less laminated structure, resulting 

 in a compact limestone, with few if any interspaces ; in others the shell frag- 

 ments have interspaces between them. Often associated with the granular lime- 

 stones are fossils which have not been previously described, aud which may be 

 new forms of calcareous algae. 



Metamorphic Limestones. 



Metamorphism by contact with intrusive igneous rocks is found both below 

 and above the latter. The limestones have become marmorised or converted into 

 crystalline calcite. 



Metasomatic Limestones 



consist of a replacement of the original limestone by crystilline silica or quartz, 

 or by the doable carbonate of lime and magnesia. 



The former results in a rock consisting entirely of quartz, The changes from 

 a limestone free from quartz, through limestones with quartz crystals and a 

 quartzose limestone to a quartz rock, may be easily traced. 



The latter change takes pla^e when the carbonate of lime has been replaced 

 by dolomite. In this case specimens can he obtained showing the various stages 

 of replacement. 



II. The Ferynian Limestones 



in the eastern part of the county consist of more or less well-defined rhombohedra 

 of dolomite with few angular grains of quartz. The white and red sandstones of 

 the same district, which apparently lie below the limestones, contain more 

 numerous angular grains of quartz in a dolomitic base, and compose about one- 

 fourth of the rock. The latter rocks may therefore be termed dolomitic sandstones 

 or quartzose dolomites. 



On the Occurrence of Native Iron in the Deccan Bascdt. 

 By Professor J. Joly, F.R.S. 



