404 FERGUSON. 



The Kaal formation. — This series of sedimentary rocks outcrops in an 

 irregular band in the western part of the area, running north from the 

 M'estern flank of Mount Vil-lon for about 6 kilometers to a point east 

 of Mount Aroroy, and occurs farther north in irregular areas near the 

 Aroroy quartz diorite formation. These sediments everywhere are the 

 least resistant of the rocks found in the area, and hence are encountered 

 only in comparatively rare outcrops, for the most part in the stream beds. 

 Between Kaal Creek and Mount Vil-lon there is a small plain at about 

 50 meters elevation, where boulders of psilomelane are found on the 

 surface. Prospecting has shown that the rock here is a very fine-grained, 

 firm, red slate, without traces of banding, containing psilomelane in 

 lenses parallel to the slaty cleavage. A similar red slate with manganese 

 is found farther north, east of the junction of Balangting Creek with the 

 Guinobatan Eiver, and also, on the oi3posite side of the Guinobatan above 

 the gorge, but here Avithout the manganese. Several outcrops of a dark 

 slate are found in Kaal Creek itself and its two small tributaries. As a 

 rule, this is faintly banded, showing poorly marked narrow bands of 

 dark and slightly lighter material. The strikes and dips are constanly 

 changing, suggesting great contortion, but as a general rule, where bed- 

 ding is observable in the rocks of this formation, the strike is north- 

 easterly, and the dips, although extremely variable, are for the greater 

 part steep to the northwest. This darker slate almost invariably is lined 

 with a minute network of quartz and calcite veins, generally not over 

 one centimeter in width and grading down to microscopic veinlets. Much 

 of the slate found in irregular areas on Lubigan and Ambulong Creeks 

 is similar to this. Another phase found in the same localities is a fine- 

 grained, dark purple slate, very similar, except in color, to the red slates 

 east of Kaal Creek. The outcrop of the Kaal formation on the coast, 

 west of the village of Aroroy, and other outcrops east of Mount Aroroy 

 show a gra}'^^acke rather than a slate. In the latter locality a grit or 

 coarse-grained sandstone occurs, the pebbles of which, where large enough 

 to be seen, all seem distorted; as far as could be discovered they are 

 composed entirely of sedimentary rock, apparently a fine-grained, dark 

 slate. No pebbles of igneous rock were found anywhere, nor did there 

 appear to be any phase of this formation which might be interpreted as 

 the basal conglomerate of the series. The most interesting outcrop of 

 this formation occurs on the point forming the western corner of Bu}Tian 

 Bay; here a dark slate, similar to that found in Kaal Creek is seen to 

 be intruded by a small stringer of quartz diorite. Not far from this the 

 slate appears to be in contact with a larger mass of diorite, although the 

 evidence of intrusion is not so clear as in the previous case. 



In the vicinty of Lubigan and Ambulong Creeks the slate is frequently 

 cut by dikes of the fine-grained igneous rocks which have been grouped 

 together in the Panique formation. The slate is clearly older than the 



