23,5 Dickerson: Baguio Plateau 415 



systems are so extensive that the soil is firmly held in a perfect 

 root mat, and erosion is consequently far less than one might 

 think from a mere study of the amount of rainfall. Certain 

 fair-sized streams in the coastal-plain region just north of 

 Grays Harbor Bay have succeeded in digging only shallow 

 valleys in the marine sediments of Pleistocene age, and but few 

 of these streams have succeeded in trenching through the sands 

 and gravels of this time to the underlying rocks. 



From his previous experience the writer was quite unpre- 

 pared to expect the conditions discovered in the vicinity of 

 Baguio. The resemblance of the effects of tropical torrential 

 downpour to that of arid and semiarid regions is noteworthy. 

 The vast amount of debris deposited by such streams as the 

 Agno and Bued as they debouch upon the central plain of Luzon 

 is, after severe typhoons which swept across this region, remi- 

 niscent of cloud-burst effects in the Mohave Desert region of 

 southern California. The writer hesitates to introduce a new 

 variant into Davis's humid cycle, but the evidence compels him 

 to conclude that quantity of rainfall is not sufficient to accele- 

 rate rapid development of topographic forms in humid tropical 

 regions, but that the torrential character of great rainfall is the 

 principal factor. 



These general studies made in the environment of Baguio 

 indicate that Luzon was visited by the same type of disastrous 

 typhoons during Pleistocene age as continue to sweep across 

 these islands at the present date. 



REVIEW OF PREVIOUS WORK 



Von Drasche 2 first made known the widespread occurrence 

 of coralline limestone which is typically exposed at Trinidad, 

 and he described the other rocks stratigraphically beneath this 

 interesting formation. 



A short distance behind Kayan mighty breccias of doleritic rocks are 

 encountered, then breccias of hornblende-sanidine trachyte, and farther 

 eastward there appears a breccia-like rock bedded in thick layers [fig. 1]. 

 The last-named consists of large and small irregular fragments of limestone 

 and of a badly weathered trachytic rock. * * * This conglomerate 

 alternates with strata of coralline limestone, very similar in every respect 

 to that found in Benguet Province. The strata show an inclination to 

 the southeast of 8°-12°. 



Again he mentions this formation near Sagada. 



Geologie der Insel Luzon, Wien 



