68 C. A. SUSSMILCH. 



The olivine preponderates and in some examples the rock 

 consists almost entirely of this mineral. The poecilitic 

 structure so characteristic of the previous rock is absent. 

 Augite is only sparingly present. The enstatite occurs in 

 allotriomorphic crystals ranging up to nearly 4 mm. in 

 diameter. The picotite occurs as small rounded granules 

 enclosed in the other minerals, but is not abundant. 



IV. Pyroxenite. Consists practically of augite only with 

 an occasional small crystal of olivine ; is phanerocrys- 

 talline and the fabric is allotriomorphic granular. 



Besides these rocks several large isolated crystals of 

 augite were found, all of which have been corroded by the 

 enclosing rock. The largest example measured 3 inch by 2 

 inch by 1 inch. 



Petrographical Description of the Monchiquite. 



a. Characters as seen in the hand specimen. 

 Colour, blue-black 



Fracture, even 



Cystalliuity, aphanitic 



Granularity, relative, even, not porphyritic 



Minerals visible, none recognisable. 



b. Microscopic Examination. 



/Crystalline, hypocrystalline 



Fabric, the olivine and augite are automorphic 

 the latter more or less lath-shaped and 

 together with the other mineral set in 

 a more or less isotropic base. 



Crainsize, average about 0*2 mm. 



Minerals present (in order of decreasing abundance) 



1. augite (titaniferous), 2. olivine, 3. magnetite, 



4. felspar, 5. biotite, 6. apatite and an isotropic 



base. 



Mr. G. W. Card gives the following description of the 



monchiquite from Dyke No. 36 : — " Under the microscope 



Texture 



