HuTTON. — (Jeolagy of North-eastern Otago. 417 



the rocks. If I had examined the Waireka Valley duriug my 

 first visit to the district I should probably have found out my 

 mistake. As the Ototara limestone is younger than the volcanic 

 rocks, the inference naturally follows that the Hutchinson's 

 Quarry beds, which also rest on volcanic rocks, may be un- 

 conformable to it ; but the stratigraphical evidence is not con- 

 clusive, as tlie Ototara limestone may, perhaps, never have 

 extended so far to the east. This question must be solved by 

 paleontology, as I will presently point out. The specific gra- 

 vities mentioned in the paper were all taken by Walker's Specific 

 Gravity Balance, and by Jolly's Spiral Balance. 



Oamaru District. 

 Volcanic Rocks. 



I noticed four principal centres of eruption, but no doubt 

 there are others. 



1. Oamaru Volcano. — In passing along the shore from the 

 breakwater at Oamaru to-wards Cape Wanbrow, we first find rocks 

 dipping 25° N. The upper beds (PI. XXVI., Section I., a), under 

 the Flagstaff, are basaltic agglomerate and ash, the former with 

 bands and pieces of fine-granied limestone. It is this limestone 

 that in 1874 I mistook for included fragments of Ototara stone, 

 altered into a kind of lithographic limestone. By Mr. McKay 

 they are shown as regular beds, interstratified with the agglo- 

 merate. A careful inspection, however, has convinced me that 

 they are all veins running between blocks of lava in the agglo- 

 merate. They are segregation veins, formed from the calcareous 

 cement in the agglomerate and ash beds, and are of later age 

 than the main body of the rock. The volcanic rocks in contact 

 with these veins are not in the least altered, and the veins are 

 usually compact and solid throughout, often with a banded 

 structure parallel to the margin. In one instance I noticed that 

 there was a compact layer on each side, while the central por- 

 tion, varying from 6 to 12 inches in thickness, was filled in with 

 broken shells and corals ; the two inner surfaces of the lime- 

 stone were quite smooth, and the organic fragments appear to 

 have been washed in from above. Associated with these beds 

 are tachylyte breccias, consisting of angular fragments of glossy 

 tachylyte, rarely exceeding an inch in thickness, cemented 

 together by crystalline calcite. Bound their margins the frag- 

 ments are often altered into a rich yellow-brown palagonite. 

 The basalt of the agglomerates is compact, bluish-black in 

 colour, finely crystalline, and with olivine more or less abundant ; 

 S.G. = 280. Under the microscope it is seen to consist of a 

 microcrystalline ground-mass of felspar laths, magnetite, and 

 pinkish-brown augite grains, containing here and there crystals 

 of shghtly dichroic olivine, much decomposed round the margins 



27 



