166 MR. J. MARTIN ON THE TERRACES OF ROTOMA.H ANA . 



Measurements along a line of radius from the lake to the summit 

 gave the following results : — 





Radial 

 measure- 

 ments. 



Elevation. Average. 



Temperature 

 of overflow. 



^Lower j % Lf)wer plateau 



^ 3. Cold-water Basins 



Middle |4. Tabular masses and 



Upper 



Terrace. Q Upper platform . , . 



ft. 

 80 



66 



150 



240 



250 

 30 



ft. 



1 or 1 in 80 

 4= 3° 5' or 1 in 16 

 10= 3° 5' or 1 in 15 



50=11° 5' or 1 in 5 



35= 7° or ] in 8 

 Level 



60° to 80° 

 80° to 90° 

 60° to 90° 



80° to 112° 



115° to 160° 

 160° to 170° 



The Great Cauldron, or Basin, when empty, appeared to be 

 an extensive excavation lined, decorated and richly ornamented 

 with the characteristic deposit of snow-white sinter. Its form was 

 elliptical, with a longer diameter of 200 feet and a shorter of 

 165 feet. 



1 The sides of the Cauldron formed a nearly vertical wall 10 feet 

 high, which extended about halfway round on the east side, the 

 other portion sloping inward at an average angle of 30° to a depth 

 of about 20 feet, except under the " Lion Rock," where a magnificent 

 cornice overhung a perpendicular wall 14 feet in height. 



The basin-floor was broken into large irregular masses, the whole 

 surface being roughly corrugated into wavy lines (probably caused 

 by convection-currents) and presenting the appearance of wind- 

 drifted snow. 



The Cauldron was enclosed by a smoothed and perfectly level 

 rim of silica, about 6 feet in average width. 



This enclosing rim formed a pathway round the Cauldron, except 

 on the south side, where its continuity was broken for a distance of 

 40 feet, being perforated by a number of small steam-holes. 



The crater-walls, excavated from the hill by hydrothermal action, 

 rose abrupt and dark from the outer circumference of the rim. 



Erom 50 feet in height behind the Cauldron this wall sloped, 

 as it embraced the hollow, to the sharp ridges which formed the side 

 of the entrance, and, with the " Lion Hock," probably, at an earlier 

 period, completed the circuit at a height of from 12 to 15 feet above 

 the level of its recent overflow. 



The opening to the upper platform in front of the Cauldron 



