The boundary with the Tollie gneiss to the Northeast was not observed. The boundary with the Luibean semipelitic schists was observed to the Southwest at Location 144 (NGR 81387753) with a sharp sub-vertical contact. As with the Tollie gneiss, the Druim breccia overlies the Garbh amphibolite with a clear angular unconformity.

The Garbh amphibolite has an outcrop width of about 550 metres.

Exposed surfaces of the amphibolite show the rock to have a dark almost black colouration with a foliation being highlighted by preferential weathering and the foliation surfaces being defined by white feldspars. The foliation surfaces (i.e. the "S" fabric) are two centimetres apart.

Fresh surfaces of the amphibolite showed the grain size to be fine grained (i.e. less than one centimetre) with an overall dark colouration. The mineralogy of the rock includes amphibole, quartz, feldspar, and ores. No mode could be identified in hand section due to the fine grain size of the rock. A thin section (Figure 4) was cut to assist in the comparison between the Garbh amphibolite and the Achlais amphibolite.

The thin section showed the grain size to be less than 0.5 millimetres and a good alignment of minerals giving an "L" fabric to the rock.

The mode of the rock was amphibole (hornblende) 45%, quartz 35%, plagioclase 10%, iron ore opaques 10%, and accessory apatite, sphene and epidote.

Folding is observed in the unit and is restricted to the Druim nan Uamh ridge around Location 111 (NGR 81957742) by an Southwest - Northeast trending fault. The structure of the Garbh amphibolite is discussed more fully in the structural section of the report,

The general trend of the foliation is striking towards the Northwest - Southeast and the dips are uniformly steep.