THE LAKES 15 



base, in close proximity to the lake, had somewhat sunk in local 

 sympathy that, in fact, the cant of the range had been in some 

 degree readjusted by the subsidence which created the lake basins. 



Local weakness in the earth's crust, break in continuity of geological 

 plan, proof in the exposed ocean-floors of many changes of elevation, 

 difference possibly in degree of eastward cant of the range contiguous 

 to the lakes, makes subsidence at any rate a tenable theory in regard 

 to the lakes of Tutira. 



Their original depths may be approximately calculated from the 

 present appearance of the ranges on either side and from examination 

 of the cachment area of the Papakiri. The valleys gouged out, the 

 sand and grit borne down, minus that percentage drained off in the 

 form of muddy water, rest at the bottom of one or other of the lake 

 basins. The area covered by Tutira lake has been in past times con- 

 siderably greater than at present, for the stream that drains away its 

 surplus water has eaten through a bank of sandy marl to the depth 

 of some twenty feet. There remain, nevertheless, no signs whatever of 

 this period a fact explicable only on the assumption that erosion of 

 the channel of escape must have been at first exceedingly rapid ; 

 that it must have been worn through not in years, but weeks, 

 perhaps days. 



Had flood -water, containing in suspension mud carried down in 

 landslips from the fertile marls of the Newton range, been deposited 

 on the receptive pumiceous lands which must have been then under 

 water, a distinct vegetation would have arisen. The effect of such 

 submersion would have been apparent still, for after heavy floods 

 the waters of the lake remain wan for months with comminuted 

 clay. 1 Such a top-dressing would, I am confident, have remained dis- 

 tinguishable in its effects to this day. If in no other way, it would 

 have been recognisable by bracken of a deeper green, by manuka of 

 a taller growth. 



The conjoined waters of Tutira and Waikopiro at present escape 

 from the north - west corner of the former. Whether they have 

 always done so remains an open question ; a 30-foot rise from the 

 present height of the lake would allow its waters to lap over in three 

 directions. These three lines of escape would be firstly, its present 



1 After the deluge of 1917, when more than 20 inches fell in four sequent days the rain- 

 gauge twice overflowing the lake had not regained its usual blue twenty-four months later. 



