MR. 0. A. DERBY ON 



peak of Picu is known, from specimens collected in. the bed of a stream 

 flowing from it, to contain a variety of types of foyaite and other 

 nepheline-bearing rocks ; and another prominent peak, called Itajuba, 

 in the same vicinity and in the same range is, judging from its 

 topographical features, of similar structure. TheBocaina locality is 

 only known to me by a specimen of foyaite brought from there 

 some years ago by the director of the National Museum when on a 

 botanical excursion. 



The Iguape region is only known to me through specimens kindly 

 furnished at various times by a German engineer, Mr. Henry Bauer, 

 who has given considerable attention to the collection and study of 

 the rocks of his district. They include several peculiar types not 

 yet known from other localities ; and suspecting that they were 

 associates of foyaite, I requested Mr. Bauer * to search for that 

 rock, which he has recently found at a place, called Jacupiranga. 

 Nepheline-bearing rocks also occur in the vicinity of Xiririca 

 further up the valley, and there are reasons for supposing that a 

 number of other localities will be found in that region. The Itambe 

 locality is only known by a specimen in the National Museum of Rio 

 de Janeiro, sent many years ago by the German geologist Eschwege, 

 under the name of diorite, and which is pronounced by Prof. Rosen- 

 busch to be a fine example of nephelinite. 



A cursory examination of some of the localities above mentioned 

 having shown an apparent and hitherto unsuspected relation 

 between foyaite, phonolite, trachyte, tuff, and certain types of basalt, 

 I determined to visit the Caldas region, from which a specimen 

 intermediate in character between foyaite and phonolite had come 

 into my hands, and where a railway under construction gave 

 unusual facilities for examining this series, while the proximfty 

 of a sedimentary formation of palaeozoic age gave hopes of ob- 

 taining some idea of its geological age. A. splendid development 

 of foyaite, phonolite, and tutf was found associated with several 

 types that have not yet been met with in the other localities. 

 The tephritic basalts which characterize the other places are repre- 

 sented by leucite-basalt and by a peculiar rock having the external 

 aspect of a diabase, in which plagioclase is the predominant element, 

 and which I suspect will prove to be teschenite. Tracirytes, if 

 represented, only appear in dykes too much decomposed for accurate 

 determination. 



The Mogyana railway, starting from Campinas in the province of 

 Sao Paulo, runs near the margin of the mountainous plateau of 

 southern Minas Geraes and the sedimentary plateau of Sao Paulo. 

 The former, composed of gneiss and metamorphic schists, has a 

 mean elevation of from 1000 to 1200 metres ; the latter composed of 

 horizontal strata of shale, sandstone, and limestone, cut by numerous 

 and large dykes of diabase, varies in elevation between 600 and 1000 



* Among the rocks sent me by Mr. Bauer is olivine-basalt (limburgite). In 

 the other two localities in which it is known (Campo Grande and Tingua) it 

 occurs also in connexion with the group of nepheline rocks here considered, 

 and it may be suspected that the relation is not purely accidental. 



