118 MR. J. ROMANES ON THE [Feb. I912, 



(ii) Sedimentary deposits of El Brazil. — In this area are 

 several good exposures of sediments which are seen to underlie the 

 lava-flow. Thev all exhibit a very shallow-water character, and in 

 many cases are richly fossiliferous. A few exposures are visible in 

 the river-banks between the cataract and the lower end of the 

 pipe-line. At the junction of the creek and the main river is an 

 exposure of some tine conglomerate, striking north 70° west and 

 dipping 35° southwards. I did not see any fossils in situ in this 

 deposit; but some large boulders of the same type, containing 

 fragments of Fecien, may be seen in the river-bed. The rock has a 

 general purple colour, with in places a white calcific matrix. Many 

 boulders more richly fossiliferous also occur in the river-bed, and 

 these evidently come from a point some 80 yards farther up stream 

 where similar rocks are seen practically in place. The exposure, 

 owing to landslides, is, however, very bad, and dip and strike are 

 not determinable. These rocks are of a distinctly greenish colour 

 and much finer-grained than the conglomerates. Lithologically 

 they are volcanic ashes, and in a slice much of the rock is seen to 

 consist of fresh basic plagioclase, together with de vitrified glass and 

 an indeterminate fine-textured matrix. These deposits are crowded 

 with fairly well preserved Pectens which are evidently closeiy allied 

 to the smaller type of Pecten in the San Miguel Limestone. 



At the intake station the sedimentary rocks are much better 

 exposed, occurring on both sides of the river. The dip here is 

 about 15° northwards, but this when the beds are traced down 

 stream soon falls off to 2^ or 3°. The lowest bed seen is a massive, 

 grey, volcanic agglomerate, containing a few highly carbonized 

 wood-fragments. The constituents of this rock are considerably 

 decomposed ; it contains numerous broken crystals of a fairly acid 

 plagioclase, together with many angular fragments of a felsitic 

 character. Above this comes about 20 feet of well-bedded fossili- 

 ferous ash. This rock is of a bright green colour, and consists 

 of broken felspar-crystals and the felsitic fragments noted above. 

 Fossils are rare, and occur principally in the lowest bed exposed. 

 They are mostly small and rather badly-preserved gasteropods, while 

 scattered through these beds occur many fragments of wood ; but 

 these are quite carbonized and show no structure. Overlying the 

 ashes is another coarse agglomerate, always extremely weathered. 

 These bedded ashes, when traced down stream, disappear below the 

 lava-flow about 200 yards below the intake-station, and the lava 

 comes right down to the level of the river. The actual junction 

 of the two is obscured by river-gravel, the lowest part of the lava- 

 flow visible being a scoriaceous volcanic conglomerate, and above 

 this the lava shows the remarkable ' bladed ' jointing mentioned 

 above. As we ascend the south side of the gorge, we find the coarse 

 agglomerate overlain by a fine -olive-yellow marl, which in litho- 

 logical character corresponds exactly with the yellow marls of Tres 

 Kios. An important point is that the northward dips are found 

 to increase rapidly to about 30°, when followed southwards from 

 the river. 



