386 PROF. P. MARSHALL OX THE SEQUENCE OF [Dec. 1914, 



"basalt, each of these being separated from those above and below it 

 by a bed of scoria, "which is in nearly all cases thicker than the 

 actual lava. The upper and lower surfaces of the lavas are highly 

 irregular, and the thickness of each flow is extremely variable. 

 The scoria is rather loose, much oxidized, and is in most cases 

 dark red, thus indicating that the eruptions were subaerial. 



Resting on the basalts is a flow of a peculiar lava about 30 feet 

 thick, with somewhat regular horizontal joints. The rock is 

 highly porphyritic, contains big crystals of hornblende and felspar, 

 with smaller ones of augite, and is covered by a thick but very 

 irregular scoria-bed. The porphyritic lava is followed by a thick 

 flow of phonolite, of the type described in my previous paper as the 

 Logan Point Phonolite (it contains much nepheline and cossyrite). 

 Scoria again covers the phonolite to a depth of 50 feet on the 

 average. 



There is then another succession of basalt-flows, this time eight 

 in number, and, as before, relatively thin and separated by thick 

 red beds of scoria. The lowest of these basalts is a bigger flow 

 than the rest, with the exception of the seventh, which is also of 

 great size. In my previous rmper on this section I represented 

 a trachydolerite, then called a basanite-lava, as situated below this 

 large flow of basalt. More careful observation, however, showed 

 that the trachydolerite does not occur in the actual face of the 

 cliff, although it is present beneath this identical basalt a little 

 farther north at Hayw T ard's Point. It is, therefore, correct to 

 place the trachydolerite at this place in the series of lavas, for it is 

 obviously absurd to suppose that each of the lavas that issue from a 

 volcano w T ould flow T over all parts of the slopes of the mountain. 

 It is, in fact, probable that the series of lavas shown in the face 

 of the cliff by no means represents the complete succession of lavas 

 that issued from the volcano, although the series certainly does 

 represent the nature of the lava that was emitted at successive 

 periods of the activity of the volcano. 



Two flow r s of basalt follow the trachydolerite, and then occurs 

 another porphyritic rock, which in some respects resembles the 

 earlier one. As before, this porphyritic type is succeeded by a 

 phonolite. wilich this time contains no cossyrite and very little 

 nepheline ; while porphyritic crystals of felspar impart to it a less 

 dense appearance than that of the other flows of phonolite. 



The actual succession of the lavas is as follows, from above 

 downwards : — 



Tit i vie ness in feet. 



25. Trachytoid phonolite 40 



Tuff 15 



24. Trachydolerite 20 



Tuff 6 # 



23. Basalt 5 



Tuff 8 



22. Basalt 40 



Conglomerate 2 



Tuff 6 



