458 ADAMS AND PRATT. 



a part of the Eastern Coidilleia of Luzon and foitn its relatively low 

 southern extension. Alabat Island is related to this region. The 

 highest elevations reach 381 meters in Bondoc head and 378 in Mac- 

 layao Mountain. The countrv^ has a number of parallel ridges due to 

 the differential erosion of the folded and faulted sedimentary beds. 

 These structures have a northwesterly trend. There are no important 

 longitudinal valleys developed between the ridges. 



Vinos lowland. — This physiographic province has no veiT distinct 

 limits. It is differentiated because of the fact that one may pass from 

 the head of Ragay Gulf to Calauag or Basiad Bay by ascending the 

 Yinas River in a hanca and making a short portage of about two hours 

 of foot-travel to the streams M-hich flow northward. The topography 

 of the area is largely disguised by the heavy growth of timber. In 

 traveling over it some low ridges are seen and the strike of the form- 

 ations is parallel with the ridges in the Ea-stem Cordillera and are a 

 continuation of the same beds. Von Drasche emphasized this in his 

 mapping and description, and stated that in a geologically recent time 

 there was a strait which connected Lamon Bay with Ragay Gulf. 

 However, this appears to be doubtful, since there are only alluvial de- 

 posits in the valleys and no recent marine fonnations exposed within 

 the area. 



Minor districts. — In addition, there are some minor physiogi'aphic 

 districts which should be distinguished, namely, the Bulan coastal 

 plain, the Soi-sogon lowland, and the Gatbo upland. 



The Bulan plain extends from near Magallanes to a point just north 

 of Butag and is a narrow belt added to the mainland by the emergence 

 of a littoral marine dejjosit consisting largely of volcanic tuff. A con- 

 siderable portion of its coast has low, vertical sea cliffs in which the 

 formation is exposed. 



The name Sorsogon lowland is applied to the isthmus which lies to 

 the east of Sorsogon Bay. It probably was once submerged and its 

 slight- relief may be due to marine erosion. Its surface is largely formed 

 of volcanic materials, some of whicli, such as, for example, the con- 

 spicuous, white pumice, evidently have their origin in the eruptions of 

 Bulusan. 



The Gatbo upland is a remnant of the formerly extensive Tertiary 

 beds which on the eastern slope of the cordillera have disappeared 

 from the mainland either through subsidence or erosion. The formation 

 is represented in the Batan Island chain. The Gatbo upland may once 

 have been an island which has been joined to the mainland by the ex- 

 tension of the superficial deposits of the Sorsogon lowland and recent 

 elevation. The surface of the upland slopes to the eastward, and on 

 the western border it reaches an altitude pf 212 meters. 



The littoral deposits at the head of Albay Gulf, on Tobaco Bay, at 



