14 FERGUSON. 



an explosion c;rater in tlie amphitheatral valley north of Itbod, are unten- 

 able. Mr. Smith ^" has discovered volcanic agglomerate of probably 

 similar age in Ilocos Norte, hence a proper explanation should include 

 both. The Babuyanes Islands have a roughly circular form and might Ije 

 considered as a large explosion crater but for the fact that they, like 

 the Batanes, are divided into an eastern volcanic group and a western 

 group of coral islands, and as in addition no such agglomerate is found on 

 Camiguin, the only island of the groiip which the writer has been able to 

 visit. From present knowledge the most that can be said in regard to 

 the origin of the agglomerate is that in pre-Miocene times enormous, 

 explosive, volcanic activity between latitudes 18° 30' and 21° north 

 built up a land mass in the region of the Batanes Islands and a consider- 

 able mass of agglomerate in Ilocos Forte near Cape Bojeador. The 

 northern part of Luzon eastward from the Cordillera Central, is as yet 

 unexplored and hence it, is impossible to say how great an area this 

 agglomerate may cover. 



FAULTING. 



The difference in structure and topography between the neighboring 

 islands of Sabtan and Ibujos is extremely strildng, the former having on 

 its western side a straight line of agglomerate cliffs, reaching an altitude 

 of about 400 meters and broken only by narrow canons, with the fall- 

 line close to the sea, and the latter being composed entirely of limestone 

 (age as yet undetermined) rising gradually on its eastern side toward 

 the west. This striking difference of material and topography, together 

 with the straight coast line of the western side of Sabtan and the trough 

 just oil the Sabtan shore, to say the least, strongly suggests a fault line 

 between the two islands, with upthrow on the east. If we accept this 

 fault on the evidence as given above and prolong it to the north and south 

 we obtain some suggestive results. Extending the line northward in a 

 direction IST. 6° 35' E., brings Isbayat (probably similar to Ibujos) to 

 the west of the line and the Siayanes and In em (neo- volcanic) on the 

 eastern side. Following the same line to the southward there is a similar 

 division of the Babuyanes Islands, the Balingtang rocks (probably vol- 

 canic), Babuyan Claro, Camiguin and the Didicas rocks all lying to the 

 east of the line, and Calayan, Dalupiri and Fuga (Babuyan) to the west. 

 This line further extended would meet Luzon at the mouth of the Cagayan 

 River. 



ALIGNMENT OF VOLCAKOES. 



The close alignment of both active and extinct volcanoes along the one 

 hundred and twenty-second meridian is remarkable. The followang are 

 the longitudes: Y'Ami Island, 121° 58'; Mabudis Island, 121° 57'; 

 Inem Island, 121° 57'; Mount Iraya, 122° 01'; Balintang Eoeks, 122° 



"Smith W. D.: This Journal, Sec. A, Gen. Set. (1907), 2, 153. 



