PLATE XXIX. 



FIG. 1. 

 OLIVINE-DIOBITE. 



CHILYERS COTON, WARWICKSHIRE. 



Magnified 50 diameters. 



The figure represents a portion of an irregular ophitic plate of brown horn- 

 blende (8) containing lath-shaped felspars (10), green alteration products and 

 magnetite. The remaining portion of the slide from which the figure is taken 

 consists of green and colourless hornblende, cloudy granular pseudomorphs after 

 felspar, pseudomorphs after olivine and calcitc in good-sized plates. 



FIG. 2. 

 DIOBITB. 



MABSTON JABET, WARWICKSHIRE. 



The minerals represented are brown hornblende (8), magnetite (5) and 

 plagioclase (10). 



The hornblende occurs in long prisms which are idiomorphic in the prismatic 

 zone, showing the forms (110) and (010). The matrix in which the hornblende 

 lies is an aggregate of perfectly fresh felspar which occurs in grains and shows 

 lamellar twinning under crossed nicols. The rocks represented in this plate have 

 been described by Mr. ALLPORT (Q.J.G.S., Vol. XXXV., 1879, p. 367), and the 

 figures have been drawn from his original slides. 



