106 Transactions. 



precipitous clifF-like wall. Its base rests on an irregular undulating tract, for 

 the most part also covered with light moveable sand, that occupies the angle 

 between the long sand-dune and the ranges before mentioned. On this 

 undulating tract may be found banks or beds, ordinarily about the width of a 

 common roadway, composed of blocks of pumice that have been brought down 

 by the waters of the river from the interior of the country. Deposited in 

 their present position, in the shape of rounded boulders, they have been 

 subjected to the cutting action of drift-sand till the upper portion of each mass 

 has been cut away, and the whole bed offers a uniformly level surface, slightly 

 depressed centrally. In this condition the beds present the appearance of 

 paved roadways, or rather of inlaid pavements. That the blocks of pumice, of 

 which they are composed, must have been originally deposited as rounded 

 boulders, is sufficiently clear from the fact that the pumice, freshly thrown up 

 by the ocean on the open beach, as well as that thrown up either by the tide 

 within the river or by the river itself beyond the limits of the tide, is 

 invariably devoid of angular form. The specimens removed from one of these 

 beds will best show how sharp an edge has been produced where the original 

 curved surface sunk in the sand is met by the intersecting line of the newly- 

 formed plane. 



Wherever the pumice has been exposed along the external margin of these 

 beds other forms may be observed, many of the blocks showing signs of the 

 tendency that sand has to cut a sharp ridge on stones so placed. In isolated 

 situations it is by no means difficult to find examples very similar to those 

 already referred to as having been found at Lyall Bay. On these a sharp 

 ridge is to be noticed — doubtless the effect of the alternate action of two 

 currents — one, probably the stronger, being the one setting in from the sea, 

 the other blowing down the river in an opposite direction. This effect was 

 very noticeable in the case of a , large isolated block, about the size of an 

 ordinary milestone, that had become firmly imbedded in the sand, and which 

 had been cut on two faces — the apex viewed laterally presenting the appear- 

 ance of a sharp point. But the specimens brought away, though on quite a 

 small scale, are sufficient to show the general form that is produced in this 

 locality under the influence of the action of drift-sand, subject to alternate 

 currents of wind. 



Art. VII. — On Local Variations of Atmospheric Pressure dependent on the 

 Strength of Winds. By J. S. Webb. 



{Read before the Otago Institute^ 22nd July, 1872.] 

 On the 2nd of December last the Field Naturalists' Club should have met for 

 an excursion to the saddle between the Water of Leith vallev and Blueskin. 



