Hutton. — The Formation of the Canterbury Plains. 469 



compelled to limit myself to my personal observations, not being 

 able to find anything definite about this silt - deposit in the 

 reports of the officers of the Geological Survey. I have men- 

 tioned the geographical distribution of the silt because it must 

 have had the same mode of origin at Oamaru and Southland as 

 on the Canterbury Plains, so that any theory respecting it must 

 be suitable to all these places. 



Its chemical composition is not yet accurately known, as no 

 analysis has been made ; but it consists of a mixture of clay 

 and fine quartz sand, with very little iron or lime in it. The 

 sand-grains are not much rounded — not so much as we should 

 expect to find in a wind-blown deposit. 



The. most remarkable thing about this silt is its capillary 

 structure ; the mass of the rock being penetrated in all directions 

 by minute tubules, very irregular in diameter, branching in all 

 directions, and anastomosing with each other. Occasionally, 

 but rarely, these tubules are filled with calcium-carbonate, and 

 in one place, on Banks. Peninsula. I found them containing 

 limonite. On the slopes of Banks Peninsula the lower portions 

 of the silt often contain small fragments of volcanic rocks evi- 

 dently derived from the hills above. These are not found in 

 the upper parts, where the deposit is thick, nor on the plains. 



Fossils are very rare. On Banks Peninsula and on the hills 

 of the Oamaru Peninsula moa - bones occur ; and inland of 

 Oamaru the skull of an elephant-seal was found many years ago : 

 it is now in the Dunedin Museum. At Raupo Bay. near Little 

 Akaloa, on the property of Mr. J. W. McHale, there are a number 

 of concretions round bones in the silt, about 100 ft. above sea- 

 level. They are numerous, and represent the remains of a verv 

 large animal. Most of them cannot now be recognised, but 

 Mr. McHale showed me one which was evidently the first phalanx 

 of the third or fourth finger of a large baleen whale. It was 

 6 in. long by 2h in. in breadth at its contracted middle. Marine 

 shells occur in abundance at the base of the deposit round the 

 Oamaru Peninsula, and a few are said by Mr. McKav to have 

 been found at Timaru. Also, at the Port Hills, near the Con- 

 valescent Home, Miss M. Bridges has found two specimens of 

 a Euthria and one of a Crepidula. 



At Lyttelton the silt is distinctly stratified near its base, and 

 occasionally the same is seen near Timaru, but elsewhere its com- 

 position is too uniform to show any division into layers. 



Now, as to its origin : It is, I think, evident that the material 

 of the silt-deposit was brought down by the great rivers draining 

 old glacier districts. It resembles closely the glacial mud which 

 fills up some of the older lakes, as in the Rakaia Valley. Com- 

 mencing a little north of the Waimakariri and ending a little 



