TACONIC QUESTION IN GEOLOGY. 153 



of the similar rocks of Bundelkhaud in India, long since described by Clanssen and by 

 Jacquemont, and of those in Russia, where several areas of Itacolumite rocks, diamond- 

 bearing like those of Brazil and India, were discovered in the southern Urals by Helmersen 

 and Hoffman.*' 



These diamond-beariuc: rocks in Bundelkhand have since been described by the 

 Greological Survey of India as the Lower Vindhyan series/' The studies of Hartt, of 

 Gorceix, and of Derby have thrown farther light on the Itacolumite series of Brazil, which, 

 according to the latter, rests rrncouformably upon the older crystalline rocks, and consists 

 in great part of quartzites, often granular and sometimes flexible, with unctuous talcoid 

 schists containing hydrous micas, chloritic and argillite beds, specular schistose iron-ore 

 (itabirite), and great masses of crystalline limestone. The resemblances, long since 

 noticed by Lieber, between this Brazilian series and the American Taconian were made very 

 evident by a collection of these rocks from the j)roviuce of Minas Geraes, examined by 

 the writer. This ancient series in Brazil has afforded no organic remains, but being 

 unconformably overlaid by older paleozoic rocks has been by Derby supposed to be altered 

 Cambrian, while others have assigned it to a pre-paleozoic age. The diamonds, (which are 

 also met with in derived rocks,) are found in the province of Diamantina in unctiious 

 banded clays of varying colors, which are derived from the subaerial decay of eastward- 

 dipping schistose beds of the Itacolumite group.*^ 



§ 204. A close resemblance between the older rocks of Brazil and those of Guiana 

 has been pointed out by .launetaz who, as remarked by Crosby, " has recognized in the 

 latter country the itacolumite, with the hydromicaceous and other schists of the former, 

 which have been connected with the Taconian system. The itacolumite of Guiana has 

 also been obserA^ed by Schomburgk." '° Farther to the north-west, beyond the mouth of the 

 Orinoco, we meet a great development of a similar series. Crosby, writing in 1880, says 

 these rocks " constitute the main mass of the great eastern branch of the Andes, or at least 

 that part of it which skirts the Caribbean sea from Caracas eastward, and is known as the 

 Littoral Cordillera of Venezuela." The Cordillera forms the Northern Mountains of Trini- 

 dad, which have an altitude of 3,000 feet, and terminates in the neighbouring island of 

 Tobago. These semi-crystalline rocks of the Spanish Main and Trinidad were studied 



" The following bibliographical references are cited from Lieber : Eschwege, Beitrage zur Gebirgskunde 

 Braziliens, Berlin, 1832, p. 174 ; Spix and Martins, Raise in Brazilien, II Theil ; also Humboldt, Gisement des 

 roches dans les deux hémisphères, pp. 89-92 ; Jacfjuemont, Voyage dans les Indes, 1828-32, Sur les grès schisteux de 

 Panna in Bundelkund, etc.; Cotta, Gesteinslehre, 1855, p. 212, and Zerrenner, Gold, Platin und Diamant Waschen, 

 etc., Leipzig, 1851. 



" Manual of the Geology of India, Medlicott and Blanford, i, pp. xxi. and 69-92. 



■*■' 0. A. Derby, On the Diamond and the Itacolumite Rocks in Brazil, 1881 and 1882, Amer. Jour. Science, xxiii, 

 97, 178, and sxiv, 34-42; and in abstract, Rep. Smithsonian Inst., 1882, p. 332 ; also Gorceix, Gisement des Diamants, 

 etc., Bui. Soc. Géol. de France, 1884, xii, 538-545. Derby supposed the Itacolumite group might be altered 

 Cambrian ; Gorceix thinks it may be Huronian. 



** W. 0. Crosby, Notes on the Geology of Trinidad, 1878, Proc. Boston Society Natural History, xx, 44-55 ; also 

 farther, on the Crystalline Formations of Guiana and Brazil, 1880, i?«?.,xx,4S0-497, in which these rocks in Trinidad 

 are described at greater length, and the relations of the Taconian and the more ancient crystalline series in North 

 and South America are well bronglit out. See, for an .analysis of these two papers, Hunt, in Report of Smithsoniaq 

 Inst, for 1882, pp. 330-333. 



Sec. IV., 1884. 20. 



