The Black Earth. 351 



the great rivers, growing exclusively on sands and other fluviatile 

 deposits. The woods which form such conspicuous backgrounds to 

 the views obtainable from Kiefi" and Sviati-Gori, over the valleys of 

 the Dnieper and Donetz respectively, are of this nature. 



Nevertheless, at the latter locality, occurs an exception which 

 appears to be of the greatest interest. D. J. Litwinoff (Moscow 

 Bull. Sept. 1891) has called attention to the fact that on the chalk 

 escarpment, which forms so prominent a feature at Sviati-Gori, and 

 at other points along the Donetz, is one of the very few occurrences 

 of Pinus silvestris known in S. Russia. Accompanying it is a great 

 variety of flowers, all of which have a distinct Alpine character. 

 The whole evidence seems to prove that these plants were already 

 living here at far earlier geological epochs, and that this small 

 remnant had been preserved during all the vicissitudes and changes 

 of Pleistocene history. 



On the other hand, the deciduous leaved trees cling to the sides 

 of the balkas and smaller streams, such as the Kalmiuss, and also 

 clothe the sides of the high right banks of the rivers already 

 referred to. Professor Krasnov points out "that the forests appear 

 to avoid the level steppes open to the influences of the winds. 

 There are, however, numerous exceptions. High watersheds, cut 

 into deep ravines, and balkas are generally wooded ; thence the 

 vegetation extends down the water-courses, in a band which comes 

 closer to the stream as the latter reaches more level regions, less 

 cut into by ravines and fissures. As researches have shown in the 

 Poltava government, the grey wood-soil follows the same law of 

 extension. This law has received but slight attention on the part 

 of students of soils." Professor Dokoutchaieflf also lays stress on the 

 fact that as fissures are formed, going over into ravines or valleys 

 of rivers, woods hasten to occupy them, and thus are gradually 

 invading S. Russia. 



Professor Kostitch on his side argues along the lines adopted by 

 Professor Whitney for the United States. He holds that the law of 

 the extension of forests depends upon the structure of the water- 

 sheds. The rains carry away the fine particles, leaving a coarse- 

 grained undersoil. The relations of coarse and fine-grained soils to 

 the absorption of rain-water are very different. In the former case 

 the water quickly descends into the deeper parts, and is retained 

 there for a long time, before it evaporates. On the contrary, the 

 fine-grained soil holds all the moisture at the surface, and allows 

 it with difficulty to penetrate. The lower-lying substratum, even 

 after strong rains, remains dry, while the upper is turned to 

 mud. From such a surface the moisture, under the influence of 

 dry winds, soon evaporates. 



On these foundations Professor Kostitch builds his wood-extension 

 theory. He believes that in the steppes the only places where trees 

 would succeed are those where a coarse-grained soil exists, in which 

 the deeply descending roots could find sufficient moisture for their 

 growth. 



Professor Krasnov considers that althousrh this view has a true 



