270 



groups. The relations of the individual constituents are those of granitic 

 rocks. None of the principal constituents shows good form. In some of 

 the specimens we find distinct indications of cataclastic structures. Bands 

 of liquid cavities sometimes traverse the quartz grains without any regard 

 to the orientation of the different individuals. The twinned felspars appear 

 faulted and bent and planes of movement, now occupied by a mosaic 01 

 quartz and felspar, may be followed for greater or less distances across 

 certain slides. 



The so-called syenites or Charnwood Forest may with propriety be 

 considered in the present connection. They are of intermediate compo- 

 sition and plagioclase is certainly as abundant, if not more abundant, than 

 orthoclase. They have been described by Messrs. HILL and BONNEY.W In 

 the southern portion of the Charnwood Forest district the rocks are well 

 exposed in large quarries at Groby, Markfield and Cliff Hill. They are 

 found also in Bradgate Park and Hammer Cliff'. Closely allied rocks occur 

 in the northern portion of the district, at Bawdon Castle, Long Cliff" and 

 New Cliff near Garendon. 



The rocks occurring at Groby, Markfield and Cliff Hill are very similar 

 in character. The dominant variety is coarsely crystalline. A fractured 

 surface is mottled with pale green, pink and black patches. Microscopic 

 examination shows that the pale green patches represent plagioclase, often 

 zonal in habit and more or less idiomorphic ; that the black patches 

 represent the ferro-magnesian constituents hereafter to be described ; and 

 that the pink patches are not individual minerals but a micropegmatitic 

 intergrowth of felspar and quartz which plays the role of ground-mass. 

 The pegmatitic character of the pink patches may sometimes be recognized 

 on a cut surtace of the rock or even on the cleavage surfaces exposed on a 

 clean fracture. The lustre of the cleavage 01 the felspar is interrupted by 

 the quartz with which it is intergrown. As a general rule the felspar of the 

 pink patches does not show multiple twinning. It may with considerable 

 confidence be regarded as orthoclase, whereas the green idiomorphic felspar 

 is probably oligoclase, as in the somewhat allied rock from Quenast (2) in 

 Belgium. The original ferro-magnesian constituents were augite, horn- 

 blende and biotite. Unaltered augite is present in most of the slides 

 examined by the author. It is colourless and closely resembles the 

 augite of the augite-granites. In some slides it shows crystalline 

 outlines but these are never very well defined. Diallagic striation parallel 

 to the basal plane is not uncommon and sometimes crystals showing this 

 striation are repeatedly twinned in the ordinary way. Clino-pinacoidal 

 sections of such crystals give the high extinction of augite and show the 

 characteristic herring-bone lineation. The colourless augite is often asso- 

 ciated with green fibrous uralite or chlorite. The original hornblende, so 

 far as the observations of the writer enable him to judge, was less abundant 



(1) Q.J.G.S., Vol. XXXIV. (1878), p. 199. 



(2) VALLEE-POTTSSEN KT RENARD. Memoire sur les characteres mineralogiques et strati - 

 graphiques des roches dites plutoniennes de la Belgique et de 1'Ardenne Fran<jaise, publ. par 

 J'Acad, Boy. Bruxelles, Tonie XL. 



