The two verniers on the azimuth circle having been read, the magnet is then inverted, i.e.
These may be used in either the upright or the inverted position.
4 represents the inverted image seen in the telescope.
In descending order they embrace the following subdivisions, whose thickness in the district of Durness is estimated at about 2000 ft.: (e) limestones, dolomites and cherts, with numerous organic remains; (d) grit and quartzite, with Saltarella and Olenellus (Serpulite Grit); (c) calcareous shales and dolomites, with many annelid casts and sometimes Olenellus (Fucoid Beds); (b) Upper Quartzite, often crowded with annelid pipes (Pipe Rock Quartzite); (a) Lower Quartzite - their original upper limit can nowhere be seen, for they have been overridden by the Eastern Schists in those gigantic underground disturbances already referred to, by which these rocks, the Archean gneiss and Torridonian sandstone, were crumpled, inverted, dislocated and thrust over each other.
Al, alimentary canal; at d, the jaws; at a, the mouth; therefore a to d is stomodaeum, whereas in the Gastropod (F) a to d is inverted body-surface.