124 THE ROCKS OF THE MADEIRA CATARACTS, ETC. [Feb. 1906. 



Pig. 3. Section of granite-porphyry from the Salto do Girao, Eio Madeira ; 

 magnified 17 diameters. Ordinary light; showing corroded quartz, 

 decomposed albite, and groundmass. (See p. 105.) 



4. Section of basalt from Theotonio, Eio Madeira; magnified 51 



diameters. Polarized light without analyser ; showing three spherical 

 spaces filled with chlorite and a lime-magnesia-iron carbonate, a 

 portion of a decomposed labradorite-crystal, and groundmass. (See 

 p. 109.) 



5. Section of pyroxene-granulite from the island below Santo Antonio, 



magnified 24 diameters. Showing pyroxene, sphene, and hornblende ; 

 the clear material is felspar and quartz. (See p. 118.) 



6. The same in polarized light, between crossed nicols. Showing, at some 



points, only granules of the different constituents already mentioned, 

 at others shadowy felspars in which the granulitic constituents are 

 embedded as in a groundmass. 



