Cotton. — Block Mountains and a " Fosnl " Denudation Plain. 63 



just beyond the j^oint at which the Upper Aorere Valley opens to the 

 south, the Aorere Valle}- is terminated by a maturely dissected scarp, 

 certainly of tectonic origin and probably a fault-scarp, the streams 

 dissecting which supply the Aorere with a tributary of considerable 

 size, Brown's River. Though this scarp forms the boundary of the 

 Aorere Valley as here defined, and though its crest is a divide between 

 the streams of the Aorere system and those flowing westward to the 

 Tasman Sea, it does not terminate the tectonic depression of which the 

 Aorere Valley forms a part, for, beyond the scarp, which constitutes a 

 step upwards of 2,000 ft. in height, the depression is continued in a 

 south-westerly direction towards the western coast, the floor of this por- 

 tion being the plateau known as the Gouland DoAvns. The composite 

 depression as a whole may, therefore, be conveniently termed the Aorere- 

 Gouland depression. 



• \SyitBvi 



Fig. 3. — Locality map of the Aorere-Gouland area. 



The continuation of the Aorere Valley depression in the Gouland 

 Downs was recognized b}^ Bell, who regarded the depression as an ancient 

 strait in which the marine Tertiary strata found in the Aorere Valley 

 and on the Gouland Downs were deposited. Bell's explanation will be 

 referred to again on a later page. 



The geological evidence as to the fault-angle origin of the Aorere 

 A^alley has been clearly stated by McKay* (p. 10), who summarizes his 

 views in the following words: "The disposition of the rocks in every 



* A. McKay, " The Geology of the Aorere Valley, CoUingwood County, Nelson," 

 Papers and Reports rel. to Minerals and Mining, Pari. Paper, C.-ll, 1896, pp. 4-27. 



