DISTEIBUTION OF THE FOREST STAND. , 17 



varies in density with local conditions. On lower Hats, where the soil 

 is deep and black, there is a hea\y mixed timber of cedar, live oak, 

 cedar elm, hackberr}', mountain oak, shin oak, and other species. 

 This kind of timber also occupies the side gorg^es and draws leading 

 out from the main streamwiws. (PL II, fig. 1; PI. V, fig. 2.) Heavy 

 also, though more stunted, is the timber on the level uplands known 

 as '' hardscrabble," where the limestone is hard and breaks in vertical 

 fissures, as for example about McNeil, in Travis County. The same 

 is true on the flat-topped buttes, where the rock is hard and fissured 

 and the soil of good depth. Such timber-capped buttes ma3^ be 

 observed on the Colorado 10 miles northwest of Austin, and again on 

 Post Mountain at Burnet, and thence off toward the Colorado below 

 Marble Falls. AVhere a crumbh^ limestone underlies the harder cap 

 the timber ceases abruptly on the slope, the broken and unstable debris 

 of this lower formation offering no foothold except for a few of the 

 most hardy plants, like mountain cedar. Such timbered caps stand 

 out in strong contrast with the white, scantily clad or quite bare 

 slopes, and at a distance of man}^ miles one can mark the lower edge 

 of the timber line as clear-cut as if the mountain side had been artifi- 

 cialU' denuded up to the level of the harder stratum. Very often 

 the harder cap has been wholly removed from the stratum of crumbly 

 limestone, and this weathers into slopes of low gradient. Here an 

 open, dwarfed timber growth establishes itself, generally of moun- 

 tain cedar. This species, which elsewhere may be so close set as to 

 form almost impenetrable brakes, becomes on this arid and unstable 

 soil or rocky adobe a more open growth of individually rounded out 

 trees. Rareh^ does the timber occup}^ these slopes so closely but that 

 their white glare is visible through the foliage (PL I, fig. 1). That 

 these slopes, covered with loose debris, ma}^ be captured and trans- 

 formed bv woody vegetation we hope to show in a subsequent para- 

 graph. (PI. m, fig. 2.) 



Shinneries. — ^A special feature of the mixed timber covering on the 

 " hardscrabble " limestone areas is that form of growth which has 

 received the name of " shinnery." Although the shinneries are made 

 up of the mixed timber above mentioned, they are general^ thought 

 of as oak shinneries, because of the predominance of dwarf shin oak. 

 The}' are simply dense thickets which, both because the growth is 

 relativel}' new and because the conditions are more severe, are scarcely 

 more than tall shrubbery. Such, for example, is the dense thicket 

 covering many square miles of the divide between the Colorado and 

 the San Gabriel drainage valleys, in Burnet Count}^ Much of this 

 is too dense to ride through on horseback. It constitutes a favorite 

 cover for deer, and as a soil retainer and gatherer is unsurpassed. 

 Mixed with the shin oak is small live oak, mountain oak, hackberry, 



30339— No. 49—04 2 



