754 SUBANTARCTIC ISLANDS OF NEW ZEALAND. [Soils and Soil-formers. 



Adams Islands. On the ridge above Sealers' Camp, Adams Island, a considerable 

 extent of country had slipped away, leaving a perfectly bare scar in a Danthonia 

 meadow. At Circular Head, in Carnley Harbour, the effects of huge slips were 

 observed coming down through the forest to sea-level. Several sheep were observed 

 browsing on this bare place.* 



The unusual matting-together of the roots of plants growing at littoral habitats 

 (on rock, J 805-7) and elsewhere (on clay, or clay and humus, J 819-20, 816-8, 821-2) 

 deserves notice. It would seem necessary for plants to send their roots through 

 several feet of top soil in order to obtain some of the mineral nutrients lacking in 

 the overlying humus. Usually in soils there is a gradual diminution of the amount 

 of roots towards the centre of the earth — that is, the proportion of roots varies 

 inversely with the depth. "j" 



The antiseptic action of humus deserves brief mention in this chemical report. 

 The wrecked " Dundonald " survivors clambered ashore over sharp rocks, in the 

 dark, and received many minor wounds, but these rapidly healed owing to the hands 

 and feet being constantly in contact with the humus soil. The body of the first 

 mate of the ill-fated ship was buried on Disappointment Island for eight months 

 and a half, at the end of which time it was exhumed and reinterred at the Port Ross 

 Cemetery. The remains were in an excellent state of preservation. Members of 

 the expedition suffered from the usual cuts and scratches incidental to " roughing 

 it," but these all healed up remarkably quickly. 



* An excellent example of bog-slides is shown on the slopes of the rounded hill on the extreme 

 right of the panoramic view of Auckland Island (fig. 2, p. 708). The hill is deeply scarred on every 

 side visible. 



t For instance, Thiel found that at the depth of 10 in. the number of roots was 100 ; at 14 in. the 

 number was 53; at 18 in., 33; at 22 in., 25, at 26 in., 20; at 30 in., 11; at 34 in., 6; and at 

 37 in., 2. 



In a clover-field examined by John six times as many fine roots were found in the uppermost 7 in. 

 of soil as were found in the soil below that depth. 



Hellreigel gives two instances of exceptions to the general rule (Storer, iii, p. 56) that the number 

 of roots diminishes regularly with the depth. A layer of soil contained a greater proportion of roots 

 than one above it : — 



(a.) In winter wheat on low land (Storer, iii, p. 61) : The soil was rich in humus at the surface, 

 and consisted of 1 ft. of sandy loam^ below which there was from 1 ft. to 2 ft. of clayey river-loam 

 overlying clear sand. At a depth of 8 in., in the soil proper, there were found 558 root-fibres; at 

 15 in., in the river -loam, 218 root-fibres ; at 26 in., in sand, 83 root-fibres ; at 33 in., in sand, 106 root- 

 fibres ; at 41 in., water-table, no root-fibres. 



(6.) Red-clover on low-lying land (Storer, iii, p. 62) : The soil consisted of sandy loam 3 ft. deep, of 

 which the uppermost 18 in. contained humus. Below the sandy loam there was from 3 ft. to 3-5 ft. 

 of clayey river-loam, and below that clean sand. At a depth of 9 in., in the loam, there were found 

 729 root-fibres ; at 20 in., in the sandy loam, 87 root-fibres ; at 24 in., in the sandy loam, 56 root-fibres ; 

 at 32 in., in river -loam, 34 root-fibres ; at 40 in., in river-loam, 32 root-fibres ; at 43 in., in the sand, 

 74 root-fibres ; at 51 in., water-table, no root-fibres. 



In both of these instances a considerable number of roots were developed in the lower moist sand 

 after the plant had been at the trouble of pushing through the clayey loam of the subsoil. 



Korticheff (quoted by Hilgard), in the black earth of Russia, " tchernozem," found a gradual 

 decrease of roots with increasing depth, in close correspondence with the humus content of the dif- 

 ferent layers. It is pointed out that the surface soil may contain less humus than the subsoil, and, we 

 may infer, less roots, where the surface soil is porous and favouring slow combustion, the conditions 

 of normal humification being fulfilled at a lower depth. 



