220 Annals of the Carnegie Museum. 



the surface of Permian sandstone. The trap is a pyroxene-bearing 

 rock, with plagioclase, but is commonly amygdaloidal and rich in 

 zeolites. It is considered to represent a later phase of the diabase, 

 and occurs in places as extensive flows. 



An example of the normal diabase was seen by the writer in the 

 valley of the Rio Poty, thirty to forty kilometers west of Marvao, in 

 Piauhy. At the base of Serra de Tucunduba in northwestern Ceara, 

 Small*^ observed an intrusion of basic igneous rock, which he took to 

 be diabase. Farther south in this State the writer crossed a band of 

 dark, basic, porphyritic rock nearly a kilometer wide, about twenty 

 kilometers north of Taua. Half-way between Arneiroz and Saboeiro 

 a narrow band of basic rock crosses the road, and twenty kilometers 

 north of Assare there is a wider band, which exhibits concentric 

 weathering. In the state of Rio Grande do Norte a band of dark 

 rock, possibly diabase, three hundred meters wide, crosses the road 

 between Apody and Angicos; and a similar band fifty meters wide 

 was noticed twenty-five kilometers farther south, between Angicos 

 and Pau dos Ferros. To the south, in the State of Parahyba, a dike a 

 meter wide, of dark, fine-grained rock, was seen near the road, ten 

 kilometers north of Barriguda. About eighty kilometers to the 

 southwest or three kilometers west of Nazareth, a band a few meters 

 wide of dark rock, which was noted as 'gabbroid,' crosses the road. 

 The seven occurrences noted by the writer in Ceara, Rio Grande do 

 Norte and Parahyba are at the only places where basic materials were 

 noticed by him, though watch was kept for such rocks. Hence the 

 statement seems warranted that basic dike-rocks are not common in 

 the region. No such occurrences were noticed in the State of Bahia, 

 but so careful watch was not kept for them there. 



Near Massape, in northwestern Ceara, there is an area of basalt, 

 which is crossed by the main road to Sant' Anna. Along this road 

 the basalt extends from four and one-half kilometers east of Massape 

 for seven kilometers northeastward. The limits of the flow to the 

 northwest and southeast are not known to the writer, but the extreme 

 length or width of the lava-covered area is probably not more than 

 ten or twelve kilometers. Along its western border, where the lava 

 overlies sandstone (probably a basal portion of the Cretaceous rocks 

 of Serra Grande), the sandstone is hardened, as if baked. The only 

 other occurrence of similar lava that the writer knows of in the region 

 <' Publ. No. 32 of the Inspecloria, p. 49. 



