GEOLOGY OF CENTRAL MINAS GERAES, BRAZIL 365 



The name Itacolumi is an old one in geological literature and 

 has been variously applied by different writers. As far back as 

 1822 Eschwege proposed the name itacolumite for a quartzose 

 talco-micaceous rock which he found abundant in, and characteris- 

 tic of, the gold and diamond fields of the Serra do Espinhago.^ 

 Eschwege himself recognized that the rocks to which he gave the 

 name itacolumite were not a unit, and in consequence noted two 

 groups, one schistose and the other massive, but he lumped together 

 under the general name of itacolumite all the quartzose rocks of 

 the region, which has been an incubus on Brazilian geological 

 studies.^ 



For a long time these rocks were generally regarded as belonging 

 to the primitive igneous crust of the earth,^ but later geologists have 

 shown them to be clearly metamorphosed sediments. By the more 

 recent writers (Derby, Gorceix) the two divisions of the original 

 itacolumite have been considered to be independent formations.'* 



While the term itacolumite has been variously applied to the 

 quartzites and quartz schists of the Serra do Espinhago, it also has 

 been used as a petrographical term to designate the peculiar flexible 

 sandstone, or quartzite, which is an oddity found at several points 

 in the district.^ But this property of flexibility is characteristic of 

 only an insignificant portion of the whole formation.^ If the term 

 be retained for the future, its only proper place would seem to be as 

 the petrographic name for this flexible phase of the quartzite, for 

 there seems to be little reason for applying a single mineralogical or 

 petrological term to such a great and varied succession of metamor- 

 phosed sedimentary formations as are now found to make up the 

 Backbone Range. 



^ Wilhelm von Eschwege, cited by O. A. Derby, "On the Accessory Elements 

 of Itacolumite, and the Secondary Enlargement of Tourmaline," Am. Jour. Sci., 

 V (1898), pp. 187-92. 



2 O. A. Derby, "The Serra do Espinhago, Brazil," Jour. GeoL, XIV (1906), foot- 

 note, pp. 374-75- 



3 A. de Lapparent, Traiie de Geologic, 2d ed., 1885, p. 654. 



4 O. A. Derby, Am. Jour. Sci., V (1898), 187. 



s E. S. Dana, Textbook of Mineralogy, p. 190. 



^O. A. Derby, "On the Flexibility of Itacolumite," Am. Jour. Sci., 3d ser., 

 XXVIII (1884), 203-5. 



