KEPHELIXE-ROCES LN BEAZII. 



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in general appears quite homogeneous, but in many places shows 

 layers and patches of pebbles up to the size of a hen's egg. The 

 pebbles could not be certainly recognized, but the most abundant 

 appear to be similar to the diabase-like rock of the conglomerate 

 at the foot of the mountain, only finer-grained and somewhat 

 altered, so that only lath-shaped felspars could be made out with 

 certainty. This tuff further resembles that associated with the 

 conglomerate by the presence of rare and small flakes of brown 

 mica. It is cut by small dykes of phonolite, and by dykes about 

 20 centimetres wide, too much decomposed for recognition, but 

 which appear to be of a basic rock. One mass which I had noted 

 in a field as a dyke, one metre wide, of a basic rock, proves on exami- 

 nation to be composed mainly of granular quartz and magnetite, and 

 is probably not a dyke, though it certainly presents the appearance 

 of one. The tuff is also traversed by horizontal vein-like masses, 

 from one to two inches thick, of a highly felspathic rock of granitic 

 or coarse porphyritic texture, and by vertical dykes, from 3 inches to 

 2 feet wide, of a rock that appears to be a more crystalline variety 

 of that of the horizontal dykes or sheets. In the largest of these 

 dykes, which is much decomposed, the felspar crystals attain the 

 diameter of an inch. In aspect this rock resembles the felspathic 

 veins of granite and gneiss much more than it does the foyaitie 

 rocks of the region in which it occurs. Under the microscope it 

 differs markedly from any rock known to me ; but I suspect that it 

 will prove to be an augite-syenite, or perhaps a liparite. Whatever 

 it may be, it, with the phonolite dykes, serves to connect the tuff 

 with the crystalline rocks of the region. 



Close by the Cascata station there is a small cutting in decomposed 

 quartzite intercalated between two cuttings in tuff. The rock is so 

 decomposed and broken by joints that its position could not be satis- 

 factorily determined, but it appears to dip to the eastward at an 

 angle of about 20°. It is cut by small dykes of phonolite and by 

 very thin irregular veins of pegmatite, showing large quartz-grains 

 and kaolin in the form of felspar, which I take to be different 

 from the felspathic dykes and layers in the adjacent mass of tuff. 

 In appearance the rock is not very unlike the sandstone at the foot of 

 the mountain ; but its occurrence at a much higher level, the presence 

 of granitic masses apparently distinct from the eruptive group that 

 characterizes the region, and, above all, the occurrence in similar 

 conditions at another point, to be described below, of undoubted 

 itacolumite, lead me to refer this exposure to a series much older 

 than that represented at the foot of the mountain. 



At Cascata the road leaves the wooded slope of the valley of the 

 Quartel and enters the Campo region of the mountainous plateau of 

 Caldas. This plateau extends northwards some 15 or 20 miles to 

 the Bio Pardo, which, where I crossed it, flows at an elevation of 

 875 metres. The mean elevation of the plateau is about 1200 metres, 

 the undulating surface presenting differences of level of from 100 

 to 200 metres. It is bounded on the west and north by an approxi- 

 mately semicircular arc of ridges rising abruptly from 200 to 400 



