42 Trcnisacfions. 



When traced along the outcrop the limestone bands are found to occur 

 as short lenses. Band A is a lens about 450 yards long, and bands B and C 

 peter out in a distance of 70 yards. 



Like the blue crystalline limestone at Dunback, the Hampden limestone 

 bands occur in the semi-metamorphic rocks of the Kakanui series of Hector, 

 the age of which is still unknown. The relationship of the Hampden and 

 Dunback limestones can be determined only by a detailed survey. 



The Hampden limestone is a fine-grained grey marble of good quality. 

 The larger blocks will form good building-material, and the small pieces 

 may be utilized for grinding into material for agricultural purposes. 



An average sample of marble from the lens marked A on the 

 accompanying sketch was analysed at the Dominion Laboratory, Wel- 

 lington, with the following results : — 



Insoluble in acid . . . . . . . . 0"86 



Alumina and iron oxide . . . . . . 0'55 



Magnesium carbonate . . . . . . 0"56 



Calcium phosphate . . . . . . . . 0"17 



Calcium carbonate (CaCOg) by difierence . . 97*86 



100-00 

 I am indebted to the Director of the Geological Survey for obtaining the 

 above analysis for me. 



Art. VI. — A Preliminary Investigation of the Age and Manner of 

 Growth of Brown Trout in Canterbury, as shown by a Microscojyic 

 Examination of their Scales. 



By M. H. CtOdby, M.A., B.Sc. 



{Read before the Philosophical Institute of Canterbury, 4th September, 1918; received by 

 Editor, 20th September, 1918 ; 'issued separately, 14ih May, 1919.] 



Plates I-VL 



The possibility of determining the age of fish by a microscopic examina- 

 tion of their scales was first demonstrated in 1899 by Hoffbauer (3), who 

 made a special study of carp-scales. 



The same principle was applied to salmon-scales by Johnston (4) in 

 three papers published in the 23rd, 25th, and 26th Annual Eeports of the 

 Fishery Board for Scotland. Johnston further demonstrated that it was 

 possible to trace the whole life-history of a salmon from its scales, and to 

 say with tolerable certainty how long the fish had spent in fresh water as 

 a " parr," at what age it had become a " sniolt " and migrated to the sea, 

 whether it had re-entered fresh water to spawn, and, if so, the approximate 

 dates of its re-entries and returns to the sea. 



Working on the same lines, Dahl (1) made a most careful study of salmon 

 and trout scales in Norway, and showed that, in addition, it was possible 

 to calculate with considerable accuracy the length attained by the fish 

 each year of its existence. 



The fundamental fact on which these investigations are based is that 

 carp, salmon, and trout — and, indeed, most if not all kinds of fish — each year 



