332 Trcmsactions. 



I referred briefly in my note on tlie Lake Heron spits to their peculiar 

 form, which appeared to be a fairly common feature, if one can judge from 

 the frequency with which spits of similar shape are figured in publications 

 dealing with the physiography of lake-shores. This I attributed directly to 

 wave-action, for when watching the waves coming down Lake Heron before 

 the strong north-westerly wind I noticed that when they broke on the 

 spit they were invariably parallel to its shore, the change in the direction 

 of the wave-front being due to the retardation produced by the pronounced 

 friction of the bottom in the shallower water near the beach as compared 

 with its comparatively slight eiltect in the deeper water off shore. The 

 form of the spit, with its general convex curve lakewards, is therefore that 

 of the involute of the different wave-fronts as they break, so that it must 

 have an intimate mathematical relation to the circumstances determining 

 the formation and speed of waves in the immediate vicinity. Unfortunately, 

 I have not sufficient knowledge of mathematics to tackle such a difficult 

 problem, and I cannot demonstrate the exact curve which should result 

 from its solution, although I am confident that it should be obtainable by 

 mathematical methods, and the result would confirm the inferences drawn 

 from observations in the field. 



The present note is intended to draw attention to a hooked spit occur- 

 ring in Lake Coleridge whose formation appears to me to be entirely due 

 to wave-action. 



(Situation and General Surroundings. 



The spit to which I wish to refer particularly is situated in the south- 

 west corner of Lake Coleridge, about a mile from the Lake Coleridge home- 

 stead. At its proximal end, where it is joined on to the solid land, there 

 is a roche moutonnee with distinctly striated and fluted surfaces, and on 

 its extreme point grows the rata-tree made historical by references in Lady 



Z/!/fZ: COLER/DCE 



■Q^ierSpjL.^6^^^ 



Sketch-plan of the Shingle-sfit.s in Lake Coleridge. 

 (Scale, 10 chains to an inch, approximately.) 



Barker's " Station Life in New Zealand." It is satisfactory to note that 

 this tree is still flourishing, although it is the only one growing on that part 

 of the lake-shore. From this tree stretches first of all a true beach, and 

 then the free portion of the spit, about 20 chains in length. The spit varies 

 in width up to about 3 chains. About half-way along it divides into two, 

 the outer part being of recent formation and separated from the parent 



