THE GEOWTH OP THE TUNDRA. L27 



The depth of the humus layer beneath the moss was found to be about two 

 feet, at St. Michaels. A mile east of the village it was about twelve feet. In 

 the delta of the Yukon a depth of over fifteen feet was seen at one locality. 

 As satisfactory sections are rare, these measurements do not indicate its 

 average thickness. A depth of 150 to 300 feet has been assigned by several 

 observers to the tundra where it is exposed in a sea-cliff on Eschscholtz bay, 

 at the head of Kotzebue sound. This interesting locality has received more 

 attention than any other similar portion of the shore of Alaska, owing to the 

 fact that the ice is there well exposed and the surface layer of humus is rich 

 in mammalian remains.* 



Ice cliffs similar to those in Eschscholtz bay, but of greater extent, occur 

 along the Kowak river, which empties into Kotzebue sound. These ice 

 deposits have been described and illustrated by J. C. Cantwell,f who sug- 

 gests that they may be the remnant of a frozen river. 



The explanation of the formation of the tundra is to be found in the fact 

 that its vegetable covering grows at the surface and dies and decays below, 

 but is frozen before complete decomposition takes place. The surface of the 

 frozen substratum rises as the thickness of the protecting carpet above is 

 increased. There is apparently no reason why this process might not con- 

 tinue indefinitely, so as to store up vegetable matter in a way that is only 

 paralleled in the most extensive coal fields. 



A possible Origin of Coal Seams. — So vast is the amount of vegetable mat- 

 ter now imprisoned in the tundra of the North, that I venture to suggest that 

 possibly some coal seams may have had a similar origin. 



This suggestion does not seem so very unreasonable when one remembers 

 that except in the circumpolar tundra, deposits of vegetable matter are no- 

 where accumulating at the present day to anything like the extent or thick- 

 ness required for the formation of coal-fields like the one, for example, of 

 which Pennsylvania still retains a remnant. Botanists will say at once, in 

 opposition to this suggestion, that the flora of most of our coal-fields, and 

 especially those of Paleozoic age, indicate tropical or sub-tropical conditions. 



* Descriptions of this locality may be found in the following books: 



Otto von Kotzebue : A voyage of discovery into the South sea and Beering's straits, for the pur- 

 pose of exploring a northeast passage. Undertaken in the years 1815-1818. London, 1821, 8vo, vol. 

 1, pp. 219-220. 



Captain Beechev : A narrative of the voyage and travels of Captain Beeohey, R. N., F. B. 8., &c, 

 to the Pacific and Bearing's straits; performed in the years 1825, '26, '27, and '28. London, 8vo, 

 pp. 372-377. 



W. H. Dall : Extract from a report of C. P. Patterson [On Coast Survey work in Alaska]. Am. 

 Jour. Sci., 3d ser., vol. 21, 1881, pp. 104-111. . , 



C. L. Hooper: Report of the cruise of the U.S. Revenue-steamer Corwin in the Arctic Ocean [in 

 1880]. Treasury Department, Washington, 1881, 8vo, pp. 24-25. 



C L Hooper: Heport of the cruise of the U. S. Revenue steamer Thomas Corwin, in the Arctic 

 Ocean. 1881. Treasury Department, Washington, 1884, 4to, pp. 79-81. PI. op. p, so 



VV. H. Dall: Glaciation in Alaska. Bull. Philosophical Society of Washington, vol. 6, 1884, pp. 



t A narrative account of the exploration of the Kowak river, Alaska; in Reporl of the Cruise of (he 

 Revenue Marine Steamer Corwin in the Arctic ocean in the year 1885, by Capt. M. A. Bealy, 

 Treasury Department, Washington. 1887, pp. 48-49, and plates op. p. 48. 



