part 1] AXD ASSOCIATED BOCKS OF MOZAMBIQUE. 49 



The forsterite-marble has considerably influenced the later 

 intrusive rocks which have come into contact with it, and these 

 will be described in later sections. Two contact-rocks, however, 

 may be described more properly in this place. 



At the south-eastern termination of the limestone (near the dip- 

 arrow on fig. 4), a skarn-like rock (Wo. 193) occurs between 

 amphibolite and the limestone. The minerals of the rock 

 (PI. VIII, fig. 6) are chiefly garnet, scapolite, and quartz. 



Garnet is the most abundant mineral, and in thin section is nearly colourless 

 or of a pale pink. Qualitative tests indicate the presence of lime in consider- 

 able amount, with magnesia in less amount, and barely a trace of iron. The 

 scapolite present has a birefringence about twice that of quartz, and has 

 a much lower refractive index than the meionite of the crystalline lime- 

 stone, the value being about 1"56. It is therefore a variety having the 

 meionite and marialite molecules in about equal proportions. Other minerals 

 present besides quartz are calcite, sphene (sometimes developed between 

 calcite and ilmenite), ilmenite (somewhat altered to leucoxene), pyrite in 

 small amount, and inclusions of zircon and apatite in scapolite. The complete 

 absence of potash-felspar is a significant fact, and will be discussed later 

 (p. 58). (For the quantitative mineral composition, see Table VI, p. 59.) 



West of Memba, another quartz-garnet-scapolite rock occurs in 

 contact with crystalline limestone. The rock is coarsely foliated, 

 bands rich in pale-pink garnet and bright-green pyroxene alter- 

 nating with colourless bands composed of scapolite and quartz 

 Sphene is an abundant accessory associated with the coloured 

 minerals, and clusters of zircon in minute rounded grains are 

 frequently present as inclusions in scapolite. A garnet-pyroxene - 

 scapolite rock occurs north of the Norray Mountains, and is 

 described with the other garnetiferous rocks of that district (p. 62). 



Returning to the Ampwihi. limestone, we may notice in fig. 4 

 (p. 38) that a pegmatite -dyke is shown cutting the limestone at 

 the south-eastern corner. This pegmatite (JYb. 223) is composed 

 of quartz and felspar (chiefly microcline, but with some oligoclase), 

 with occasional flakes of muscovite and biotite, and numerous big 

 crystals of titaniferous magnetite, many of them well- shaped. 



The contact-rock (No. 222) between this magnetite-pegmatite and the 

 limestone is a most interesting rock. It is composed very largely of black 

 garnet, deep brown in thin section, with interstitial felspar of the same types 

 as those of the pegmatite. Within the garnets, which are sponge-like in 

 texture, numerous patches occur in which a deep-green augite predomi- 

 nates. Usually in these patches augite and magnetite (sometimes with 

 sphene and garnet) are closely interlaced. Throughout the garnets inclusions 

 of light-brown sphene are extremely abundant. In places apatite is present, 

 and a few streaks or granular crystals of calcite still remain — generally 

 near to, or associated with, the felspars. On the pegmatite side of the con- 

 tact, quartz begins to appear and the garnet gradually dies out. 



The garnet is a titaniferous andradite (melanite), and tested 

 qualitatively it failed to give any indication of magnesium. Its 

 mode of origin in association with sphene is suggested by an 

 experiment of L. Michel Levy, 1 who produced melanite and sphene 



1 C. E, Acad. Sci. Paris, vol. cxv (1892) p. 830. 

 Q. J. G. S. No. 293. e 



