88 PRESIDENT S ADDRESS — SECTION C. 



We now return to' the Amuri limestone, which tollcws directly 

 upon the Senonian beds in north-east Canterbury, and the coastal 

 part of South Marlborough. It is not found in the Malvern Hills, 

 and districts to the south ; its occurrence in the Trelissick Basin 

 is open to doubt, but in the Waipara district it is about a hundred 

 feet thick. At the Amuri Bluff in Marlbcrcugh it is nearly seven 

 hundred feet thick. In the Clarence Valley, however, 

 where it lies on Albian beds, it is twenty-five hundred 

 feet thick. The limestone is O'f a. peculiar character. It 

 is soft and chalky only at its extreme soiuthem limit, viz., Ox- 

 ford, in North Canterbury. Further north the lower beds of the 

 limestone are the softer and more argillaceous and pass down into 

 the Piripauan mudstone. In East Marlborough, there are alter- 

 nations of hard, chalky limestone with more argillaceous bands. 

 The thin-bedded, much-jointed and indurated natunD of the lime- 

 stone gives it a very characteristic appearance. It consists prin- 

 cipally of an exceedingly fine-grained calcareous mud, with tests 

 of foraminfera and very little terriginous matter, though there is 

 revealed chemically a donsiderable amount of silica (Thomson, 

 1916). The contrast between the microscopic features ol this and 

 other Notoeene limestones will appear from Marshall's careful 

 description (1916). The lower portions of the limestone are Very 

 flinty. Thomson urges that the limestone is in large degree a 

 chemical precipitate, and that the flints are concretions therein. 

 He holds that, except for a few local instances, there is no angular 

 unconformity between the limestone and the underlying Albian 

 rocks, and believes that its great tuickness in the Clarence River 

 Valley and north thereof ^ is the result of deposition continuing un- 

 brokenly beyond the region of terrigenous sedimentation, during 

 the Cennornanian and Turonian times (though no other sediments 

 of this age have yet been proved), as well as during the Senonian 

 times, while littoral eedimentation occurred in the surrounding 

 regions bordering lands of whidh " the surface at this time was 

 still fairly diversified." As this littoral region was deepened, the 

 Amuri limestone spread over most of the area of Senonian sedimen- 

 tion but did not extend b&yond it, except at one point, where it 

 appears to transgress on to the older greywackes (Thcmscn, 1920, 

 p. 411). Chapman's (1918) determinations of the foraminifera 

 (as yet unpublished), together with the istratigraphical position, 

 suggest a Danian age for this limestone. We may note, a^se. that 

 it contains the shark's teeth Carcharodon and Isurtis (Chapman, 

 1918). It may perhaps be doubted whether the long duration of 

 very peculiar and localized conditions demanded by Thoms:in's view 

 is as probable as the simpler explanation (regression of the sea) 

 offered by Woods, of the hiatus between the probably Danian 

 fauna of the Upner Amuri limestone, and that of the Albian beds 

 beneath the limestone in the Middle Clarence Valley. Moreover, 

 as Thomson points out, we know as yet nothing of the beds upon 

 which the limestone rests between the area in which it lies on 

 Senonian beds, and that in which it lies on Albian beds. 



