BY H. I. JENSEN. 555 



These researches, and many other valuable researches, as those 

 of Dr. Washington on "The Igneous Complex of Magnet Cove," 

 etc., we cannot here review, but a thorough study of them is of 

 greatest value to any worker on alkaline rocks. 



E. South America. 



Syenites and trachytes are abundant in the Andes of Chili and 

 Bolivia but do not, to my knowledge, belong to the alkaline 

 series. However, in Brazil, rocks of true foyaitic character have 

 been detected. 



O. A. Derby* describes nepheline syenites, tinguaites, and 

 phonolites from Cabo-Frio, Campo Grando near Rio de Janeiro, 

 Tingua, Itamibe, Itajuba, Caso Branca, and Xibirica in States of 

 Sao Paulo, Rio de Janeiro, and Minas Geraes, Brazil. The 

 rocks intruded are Upper Palaeozoic limestones of Carboniferous 

 or Permian age, and overlying theua a series of sandstones with- 

 out fossils. The latter may be of Mesozoic age, but are believed 

 to be Permian or Carboniferous. 



In connection herewith it is of interest to remark that the 

 Carboniferous rocks of Brazil are for the most part horizontal 

 and undisturbed. In parts they are covered by Jurassic or Cre- 

 taceous sediments also uniformly horizontal, laid down in an era 

 of marine transgression, but land-conditions predominated 

 throughout the Mesozoic period. 



The petrological characters of the Tingua rocks have been 

 described by Franz Pr. Graeff;f others from the Provinces of 

 Minas Geraes and Sao Paulo have been described by J. Machado. J 



Many of the nepheline syenites and allied rocks of Brazil rise 

 out of biotite gneiss or Archaean schist in districts where later 

 sedimentary rocks are not known. In these cases, of course, the 

 age cannot be determined, yet there is a strong probability that 



* Q.J.G.S. J887, Vol.xliii. No.171. 

 t Untersuchung von Elaeolith-syeniten von der Serra de Tingua, Brazilien. 

 Neues Jahrbuch, 1887, Bd.ii. 



X Tscher. Min. Mitth. N.S. Vol.ix. p 318, 1888. 



