HuTTON. — On the Foliated Eocks of Otago. 361 



not uncommon. These schists are probably altered eruptive 

 rocks. 



Age of the Bocks. 



Up to the present it has been the general opinion of New 

 Zealand geologists that these foliated rocks are the metamor- 

 phosed equivalents of the Ordovician and Silurian rocks of 

 Nelson, and by the officers of the Geological Survey some of 

 the schists are considered as probably still younger. My 

 reason for holding this opinion was that the publications of 

 the Geological Survey showed these schists passing northwards 

 continuously through the Victoria, Brunner, and Lyell Moun- 

 tains to Mount Arthur in Nelson. But in 1887 I examined the 

 rocks of the Buller Eiver, and found that the schistose rocks 

 of the south were not stratigraphically connected with those 

 of the north, as I had previously supposed,* and this led me 

 to reconsider the whole question. The absence of plication, and 

 of cleavage oblique to the stratification, throughout the dis- 

 trict are sufficient proofs that the foliation is not due to crush- 

 ing, or dynamic metamorphism, while it cannot be considered 

 as a region of contact metamorphism, for the only eruptive 

 rocks are those near Queeustowu, and they have been foliated 

 along with the rest. The metamorphic action would there- 

 fore apj)ear to be due to the internal heat of the earth at 

 a very early period of its history, when the temperature- 

 gradient was much steeper than now. In other words, they 

 are, in all probability, of Archsean age, and may have been 

 deposited almost in their present condition. 



The Pre-cambrian, or Archaean, rocks have been separated 

 into two divisions. The upper of these is, in part, detrital, 

 and has been called the Huronian, or the Proterozoic, or the 

 Algonkian. The lower is altogether crystalhne, and is known 

 as the Laurentian, or the Azoic, or the Archaean in a limited 

 sense. In the Northern Hemisphere there is usually, but not 

 always, a break between these two divisions, while in all 

 cases there is a great discordance between the upper division 

 and the overlying Cambrian or Ordovician rocks. Our 

 Wanaka series can be received as the equivalent of the lower 

 division without much hesitation ; and, as there is no break 

 between it and the Kakanui series, it is more probable that 

 the latter belongs to the Archgean than to the Palteozoic era. 



Equivalents elseiohere. 



The Otago schists svfeep round to the north-west, and 

 have been traced by Sir Julius von Haast and Mr. S. H. Cox 

 as far north as the Teremakau Eiver. Beyond this point 



* " On the Geology of the Country about Lyell," Trans. N.Z. Inst., 

 vol. xxii., p. 387. 



