A RECONNAISSANCE FKOM DAVAO. 507 



but just after leaving Banglasan one or two small bowlders of a basic, 

 igneous rock were seen. For lack of any positive evidence to the contrary 

 it is supposed that these bowlders originated in the underlying con- 

 glomerate and had worked loose from the matrix on weathering and 

 disintegration. 



The descent from the divide to the Agusan Elver was made along the 

 bed of Banglag Creek. This stream is only about half a meter wide 

 near its source, but is fed by numerous branching streams, so that in the 

 7 kilometers of its course to the Agusan it grows to a stream about 6 

 meters in width and more than a meter in depth. The descent is fairly 

 uniform in grade, and the sides of the gorge it has eroded are high and 

 steep, as far as the valley of the Agusan. 



The Banglag runs over a series of strata beginning with conglomerate 

 and sandstone lying practically level near Hoagusan, then over fossilif- 

 erous clay beds striking N. 15° W. and dipping 35° northeast. These 

 beds are in turn underlaid by. shale striking N. 20° B. and dipping 

 towards the southeast, and in the Agusan Valley by a coarse, calcareous 

 sandstone, which strikes approximately N. 60° E. and dips about 35° 

 to the southeast. This last sandstone contains large fragments of marine 

 shells in a calcareous matrix. 



No evidence of marked or recent earthquake disturbances were ob- 

 served on the route followed by the party, probably because the sub- 

 sequent heavy growth of underbrush has erased or hidden the scars and 

 fissures that may have been caused thereby; however, the territory tra- 

 versed is supposed to be a region of violent seismic activity. The Bev. 

 M. Saderra Maso, S. J., in writing of the seismic center of the Agusan 

 Eiver states:' 



"This focus is possessed of great seismic activity, as is evidenced by the long 

 series of earthquakes observed and carefully recorded by the Jesuit missionaries 

 of that region since the year 1890. In June, 1891, a violent earthquake was the 

 beginning of a long and fearful seismic period. This earthquake produced most 

 serious destruction to the houses and ground; fortunately owing to the wildness 

 of the country, there was little loss of life or of property. The falling banks of 

 the river dammed it in many spots. Long and wide fissures were opened every- 

 where, especially on the hills separating the Agusan Valley from the Hijo and 

 Sahug Rivers, which empty themselves into the Davao Gulf. The earthquake 

 lasted several minutes, and during this time, says an eyewitness, the ground was 

 moving as the troubled sea. During the following months, or during more than 

 a year, the earth trembled with more or less force every day. In June 1892, 

 there was a second violent disturbance, shaking the same region and renewing the 

 havoc of the preceding year. These two earthquakes shook the Island of Min- 

 danao nearly from end to end, and were fairly perceptible in the eastern Visayas. 



"Since these dates small shocks have been more frequent in this region than 

 in any other part of Mindanao. Their cause is probably geomorphie rather than 

 volcanic. There are unmistakable signs that the southern coast of Mindanao, 



' Volcanoes and Seismic Centers, in Census of the Philippine Islands ( 1903 ) , 

 1 , 204. 



