330 SCIENTIFIC RECORD FOR 1882. 



eition that any district of altered rocks that may be discovered is of 

 ArchEean age." 



Bonuey, continuing his studies in the vicinity of the Lizards, in Corn- 

 wall, has described the crystalline schists of the region, of which he has 

 as yet published only a preliminary note. These rocks, once regarded 

 as altered Paleozoic, are shown to be Eozoic, and are by him divided into 

 three groups, the first or lowest of which consists of greenish, often 

 micaceous schists, with hornblendic minerals, which he compares with 

 the Pebidian of Xorth Wales and Angiesea ; the second group is char- 

 acterized by black hornblende, and the third or uppermost is described 

 as a granulitic group with bauds of quartzo-feldspathic rock, the last 

 two groups beiug remarkable for their display of bedded structure, and 

 the three apparently forming one continuous series, with a general 

 northwest strike. The upper portions recall the Montalbau series. 

 We shall notice further on the serpeutines found in these Eozoic rocks, 

 both in Cornwall and Angiesea, together with those of the Alps. 



W, O. Crosby has rendered a service to comparative geognosy by 

 resuming the facts known with regard to the Eozoic rocks of eastern 

 South America, where they occupy two great areas, the one north of 

 the Amazonas, extending east to the Orinoco, which includes the vari- 

 ous districts known by the name of Guiana ; and the other, and still 

 larger region, to the south of the Amazonas, which forms the highlands 

 of Brazil. This area, extending through thirty degrees of latitude and 

 twenty-five degrees of longitude, is separated from the Andean region 

 by a broad expanse of newer rocks, stretching down to the mouth of 

 the La Plata. Hartt has shown that these crystalline areas of Guiana 

 and Brazil were above the sea in the earliest Paleozoic ti mes. They may 

 be compared both geographically and geolognostically with the Lauren- 

 tides and the Atlantic belt of Xorth America. The older observations 

 of Darwin, Pissis, and Liais with regard to these rocks are confirmed by 

 the later ones of Hartt and of Derby. The basal rocks of the Bra- 

 zilian highlands are gneisses, often granitoid, with crystalline limestones, 

 oceasionally serpentinic, with Eozoon. To these succeed a fine-grained 

 gray gneiss or leptinite, often schistose, followed by mica-schists and 

 gneisses, with subordinate beds of quartzite. The two types correspond 

 to the Laurentian and Montalban, respectively. Elsewhere in south- 

 ern Brazil are found large areas of petrosilex rocks, and of others having 

 the characters of Huronian. These same great types are also recog- 

 nized in the Andes, from Peru to Patagonia. 



In Guiana, in like manner, there is found a series of gTanitoid and 

 gneissoid rocks, compared by Jannetaz to the older gneisses of Brazil. 

 To these succeed a great series described as felstones and quartzifer- 

 ous porphyries, which are probably the same with the petrosilexes of 

 southern Brazil. Accompanying these in Guiana is a series of horn- 

 blendic and schistose rocks having the characters of the Huronian, suc- 

 ceeded by a newer series, described as resting in different places upon 



