Thomson. — Glacial Action in Otago. 321 



esteemed a circumstance of high geological importance and interest, and 

 contribute to throw some further light on the physical construction of our 

 globe. I named it ' Mount Erebus,' and an extinct volcano to the eastward; 

 little inferior in height, being by measurement 10,900 feet high, was called 

 ' Mount Terror.' " 



Again : " At 4 p.m. (January 28th, 1841), Mount Erebus was observed to 

 emit smoke and flame in uniisual quantities, producing a most grand spectacle." 



Again : " We made good progress to E.S.E., close along the lofty, perpen- 

 diciilar cliffs of the icy barrier. It is impossible to conceive a more solid- 

 looking mass of ice ; not the smallest appearance of any rent or lissui'e could 

 be discovei'ed throughout its whole extent, and the intensely bright sky beyond 

 it plainly indicated the great distance to which it extended to the southward." 



Again : " This extraordinary barrier of ice, of probably more than a 

 thousand feet' in thickness, crushes the undulations of the waves, and dis- 

 regards their violence. It is a mighty and wonderful object, far beyond 

 anything we could have thought or conceived." 



Such is the descri})tion by an experienced arctic and antarctic voyager of 

 a land such as New Zealand had once been in the glacial epoch, and I beg to 

 refer you to page 232, vol. 1, of his work for an admirable drawing of the 

 south polar barrier of ice which he discovered, and which rises 160 feet above 

 the sea level, being also 1000 feet thick and 450 miles in length. With these 

 facts before it, then, the mind may be presumed to be in preparation to perceive 

 how the great erosions of surface had taken place here. The effects we see, 

 and the power, indeed, is undeniable ; for within six days' steaming from this 

 we have the very extremes of the terrene glaciers, which have for ages been 

 subject to the melting influence of the sea, yet maintaining a thickness of 

 1,000 feet, then in the valleys and at the mountain bases we have a right to 

 conclude that in such places the glaciers may exceed 2,000 to 3,000 feet in 

 thickness. Such being the case, then, the eroding force is only a matter of 

 mere rule-of-three calculation, as below : — 



Ice weighs 591bs. per cubic foot. Ice, then, 1,000 feet in thickness will 

 have a crushing power of 409Ibs. per square inch ; of 2,000 feet, 818K)s. ; and 

 of 3,000 feet, l,227Ibs. Now, chalk, according to Rankine (which has about 

 the consistency of Caversham limestone), is crushed under a weight of 330Ibs. 

 per square inch. Thus, in the glacial epoch, would the Kaikorai Valley be 

 scooped out by nature in as easy a manner as the potter's tool shapes the clay 

 vessel. Limestone, such as most of that to be found on the Oamaru Plains, 

 crushes under 2,200fi)S. per square inch ; this, then, with the alternate clays 

 and soft shales, under half or third of the pressure, would yield to the glaciers 

 of the thickness above given when in motion ; and, when not in motion, yet the 

 more readily by the power of water, under hydraulic pressure, finding its way 



Yl 



