Fox. — The Waitemata Series. 461 



of the bed. Next to this main band the lowest layers are 

 the coarsest, those above shading off very gradually into a 

 tufaceous sandstone. From these facts it seems probable 

 that the main outburst took place some little while after 

 the vents had become active, and was succeeded by out- 

 bursts less and less powerful. The thickness of the bed 

 varies, of course, with its distance from the source : the 

 thickness' seems to average about 25 ft. at ten or twelve 

 miles from the Waitakerei Range. When we consider the 

 thickness (3 ft.) of the ash which the violent outburst of 

 Tarawera produced in 1886,* we cannot but be impressed 

 with the magnitude of the eruptions necessary to lay down 

 this coarse and thick breccia. The fossils contained in the 

 bed are generally found either at the top or bottom. 



The bed weathers to a black or brown colour when 

 exposed to the air, but in the finer parts is bluish-grey on 

 a fresh fracture. The surface is very irregular, owing to 

 the fact that the lava fragments weather out of the matrix. 

 Near vegetation — along the top of a cliff, for instance — all 

 the colour is generally leached out, the result being a 

 creamy loam ; or, if there has been much oxidation, a 

 bright-red stratum forms a band along the summit of the 

 cliff. Zeolite veins running through and through the bed 

 are not uncommon. These veins are not more than j^in. in 

 width, but extend for yards, and when the rock is weathered 

 they sometimes stand out on the face of the cliff like a net- 

 work of miniature dykes. 



The material of which the bed is composed consists 

 almost entirely of rounded fragments of lava set in a matrix 

 of hner volcanic debris. Sometimes the fragments are rough 

 and angular. Occasionally blocks of sandstone or shale are 

 included, and these are sometimes several feet in diameter. 

 Some small fragments of porcellanite also occur. 



Besides these constituents there are very numerous crystals 

 of feldspar and augite, sometimes broken, but often retain- 

 ing very perfect crystalline shape. These, no doubt, were 

 separated from the lava in which they were contained at the 

 time of the explosions. The feldspars are bright glassy forms 

 in little oblong crystals, showing good cleavage. The augite 

 crystals are of two sizes. The smaller and less perfectly 

 formed resemble those in the lava ; but occasionally much 

 larger forms may be found up to 1 in. in length, distinguished 

 from the former both by their larger size and more perfect 

 crystalline form. Large crystals, and especially large augite 

 crystals, appear to be frequently observed in tuffs deposited 

 at no great distance from a vent. Their origin is obscure, and 



* " Eruption of Tarawera," Professor A. P. W. Thomas. 



