0. A. Derby— Monazite as an Element in Rocks. Ill 



erals nearly free from titaniferous iron and garnet when these 

 are present. The separation of the zircon is presumably 

 favored by the minute size of the grains and by their pris- 

 matic form as it remains behind minerals as heavy or even 

 heavier than itself when, as is generally the case, these are in 

 larger grains. The yellow mineral, however, is frequently in 

 as large grains as the titaniferous iron and of a similar rounded 

 form and appears to hang back in virtue of its greater specific 

 gravity. A few tests were made with fused chloride of lead 

 (sp. gr. 5), which on cooling showed the yellow grains at the 

 bottom of the ingot while the zircon and titaniferous iron 

 were near the top. A number of the samples were tested 

 with the hand spectroscope giving the didymium band, but 

 owing to the difficulty of bringing together a sufficient num- 

 ber of such minute grains to give a perfectly satisfactory test, 

 this means of identification was abandoned in favor of micro- 

 chemical processes. All of the samples have been tested by 

 treatment with sulphuric acid and molybdate of ammonia. 

 In some cases crystals appeared in the sulphuric and oxalic 

 acid solutions, along with those referred to cerium, which 

 probably represent some other elements. It is possible that 

 a more complete chemical and crystallogical study of the yel- 

 low grains of these residues may prove some of them to be- 

 long to minerals other than monazite, but in the impossibility 

 of making such investigations here, they are all referred pro- 

 visionally to that species. Samples of rock and residue from 

 the granite of the Serra do Tijnca in the outskirts of Eio de 

 Janeiro, in which the yellow grains are particularly abundant, 

 have been placed in the hands of Prof. George H. Williams of 

 Baltimore, in the hope that he may find them of sufficient in- 

 terest to make such studies as, from the lack of appliances and 

 the necessary training, are out of the question here. 



The gneisses examined were obtained from a score or more 

 points in and about the city of Rio, including porphyritic, 

 granulitic and schistose varieties ; from Kilometer 78 (ascent 

 of the Serra do Mar), on the Dom Pedro II. railroad, and the 

 station of Barra do Piraley on the same line ; the station of 

 Socego on the Uniao Mineira railroad in the province of Minas 

 Geraes ; and the towns of Cutia, Piedade, Santos and Iguape 

 in the province of Sao Paulo representing an extension 

 of about 300 miles along the axis of the great gneiss 

 region of the maritime group of mountains of Brazil. In 

 every case zircon and the yellow mineral were found there, 

 proving to be the most constant accessories since ; of the ordi- 

 nary accessory elements, garnet, rutile and the iron minerals, 

 magnetite and ilmenite — the first two were frequently absent, 

 while rarely only one of the iron minerals seemed to be pres- 



