266 STUDIES FOR STUDENTS 



eighteen inches at St. Michaels to thirty-three inches at Fort Alexander, 

 the precipitation occurring largely as rain and from May to October.' 

 Russell, speaking of the tundra as developed upon the delta of 

 the Yukon and the south, says : 



General characters. — The tundra in typical localities is a swampy, moderately 

 level country, covered with mosses, lichens, and a great number of small but 

 exceedingly beautiful flowering plants, together with a few ferns. The soil be- 

 neath the luxuriant carpet of dense vegetation is a dark humus, and at a depth 

 exceeding about a foot is always frozen. On its surface there are many lakelets 

 and ponds surrounded by banks of moss even more luxuriant than on the general 

 surface. It is not always a level plain, however, but is frequently undulating 

 and may surround and completely cover hills of considerable elevation. The 

 dense tundra vegetation also extends up the mountain side and occupies the 

 entire region where the conditions are favorable for its formation. At the locali- 

 ties where I examined it the whole surface, excepting the faces of steep cliffs 

 and the summits of high mountains, was covered with the same dense brown 

 and green carpet. The characteristics are the abundance of mosses and lichens 

 and the absence of trees. Cryptogamic plants make more than nine-tenths of 

 its mass. On their power to grow above as they die and decay below depends 

 the existence of the tundra. 



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. =^ 



Chemical nature of deposits of constantly rainy climates. — The 

 distinctive chemical elTects are to be noted in the absence or small 

 amount of the soluble elements, embracing iron, magnesia, lime, 

 potash, and soda, and in contrast, the presence of carbon. Owing 

 to the diminished evaporation and the constant saturation of the soil 

 of the entire flood plain, aeration and oxidation of the soil is prevented 

 while the decaying organic matter results in deoxidizing effects. 

 Where the leaching and deoxidizing actions have fullest opportunities 

 for work, as in the clay soils beneath swamps, all soluble plant food 

 may be leached out. Where the chemical effects are less pronounced 



I Cleveland Abbe, Jr., op. cit., pp. 146, 152. 



3 I. C. Russell, "Notes on the Surface Geology of Alaska," Bulletin of the Geologi- 

 cal Society of America, Vol. I, pp. 125-27. 



