meters of sediment, principally ponded between bathymetric highs. Sedi- 

 ment thicknesses on the ridge crest and flanks are also of this magni- 

 tude. 



Dredging at the western end of the trough (Coleman and Irwin, 1977) 

 recovered fresh pillow-basalts and diabase, typical of active spread- 

 ing ridges. Fornari and others (1979) also dredged typical spreading 

 ridge rocks (although heavily weathered) from the base of the northern 

 escarpment near the center of the western end (near 8. 5°N/141. 5°E) . 



To the east (near 7. 5°N/142°E) , Fornari and others dredged fresh 



pillow basalts with strong chemical affinities to the DSDP Site 57 



basalt, described by Ridley and others (1974) as a transitioaal basalt, 



high in Fe, P , and TiO , "characteristic of Oceanic islands and 

 s '25 2 



island chains". 



At a third site (near the southern escarpment at about 8.5 N/139. 5° 

 E) Fornari and others recovered the same transitional basalt together 

 with ultramafics similar in chemistry and metamorphic grade to those 

 recovered from the inner-walls of the Mariana, Yap, and Palau Trenches. 



Of the 4 DSDP holes drilled on the Caroline Ridge and its flanks 

 (Fig. 2), only two (57;58) reached basalt, which was determined to be 

 of Upper Oligocene or Lower Miocene age by Fisher and others (1971). 

 Ridley and others (1974) established a potassium-argon age of 23.5 m.y. 

 B.P. for the basalt at site 57. 



The basalt forms a smooth, flat surface similar to that found by 

 Karig (1971) west of the West Mariana Ridge, and is generally believed 

 to be a flow, since the overlying sediments at Site 57 are unaltered 



57 



