341 



through the mass. Under crossed nicols it (the matrix) usually gives a 

 micro-crystalline reaction. There is nothing, however, in its aspect in 

 ordinary light to indicate that it is a crystalline aggregate ; the boundaries 

 of the grains are totally unrecognizable. In addition to the constituents 

 already mentioned this rock contains margarites, trichites and longulites. 

 These bodies are arranged with their longer axes roughly parallel to each 

 other. They occur both in the spherulites and in the devitrified glass and 

 their parallelism has not been affected by the development of the spheru- 

 lites. They are largest, however, in the nearly colourless zone surrounding 

 the spherulites. The following is the succession of events as deduced 

 from a study of the microscopic structure of this interesting rock : 



(1) Formation of the porphyritic felspar crystals. 



(2) Development of microlites and of fluxion structures. 



(3) Development of spherulitic structures/ 1 ) 



(4) Consolidation of the residual magma as glass and the formation 

 of perlitic cracks. 



(5) Devitrification of the glass and deposition of chlorite (?) in 

 the cracks (See Figs. 1 and 2, Plate XXXIV.). 



From the same quarry as that in which the spherulitic felsophyre 

 occurs Mr. ALLFORT obtained excellent specimens of devitrified perlites 

 (perlitic felsites). 



Felsites occur in the Malvern Hills and Dr. CALLAWAY (2) has recently 

 called attention to the passage of these into micaceous (? sericitic) 

 schists. 



A quartz-felsite occurs below the Cambrian rocks of Nuneaton/ 3 

 It contains porphyritic crystals and grains of quartz (often corroded) 

 and felspar in a matrix which shows fluxion structure. Portions of 

 the mass have a brecciated aspect. 



Professor BONNEY (4) has described rhyolitic tuff's from the Charnwood 

 Forest district in Leicestershire. 



(1) According' to VOGELSANG and ROSENBUSCH the formation of ferrite in the spherulites 

 must be referred to this stage. It is due, according to these authors, to the squeezing out 

 of the iron oxide by the crystallization of the felsite. 



(2) Q.J.G.S., Vol. XLIII. (1887), p. 530. 



(3) WALLER, G.M. (1886), p. 323. KUTLEY, G.M. (1886), p. 559. 



(4) Q.J.G.S., Vol. XXXVI., p. 337. 



