112 JOURNAL OF THE ARNOLD ARBORETUM [vol. v 



and where the gray rock covers the surface. The forest consists of a 

 mingled growth of pine and broad-leaved trees, the former standing out 

 distinctly, on account of their greater height and dark foliage, from the 

 more abundant Oaks, Hickories and a few other deciduous trees mingled 

 with them. Turning to the other side, the north slope of Rich Mountain 

 is in sight. This range begins several miles farther west in Oklahoma 

 and parallels the Blackfork to the gap, where it bends sharply to the south 

 and ends in a fish-hook-like curve, a part of which is locally known as 



Mount Men 



The western 



Mount 



fork, and at its loftiest point, about eight miles west of the Arkansas- 

 Oklahoma state line, it reaches the altitude of over 2850 feet (835 meters) 

 above sea level at the Gulf of Mexico. And since this exceeds by a few 

 feet the summit of Magazine Mountain in Arkansas, it has the distinction 

 of being the highest point in the Ozark region. The forest growth on the 

 north slope is not only denser than that of the south exposures, but it 



consists 



closer 



different and much richer in species. 



As the south side of Blackfork Mountain is most accessible and has 

 in consequence been more thoroughly explored than that of the opposite 

 range, a brief description of this will be given. That quite similar condi- 

 tions prevail on the corresponding side of Rich Mountain was indicated 

 by casual inspection at several points. 



The slope on these south exposures is steep and rather uniform in 

 most places from base to summit. There are occasional outstanding 

 ledges with vertical faces, but these are generally only a few feet in height, 

 and the angle usually does not exceed twenty or thirty degrees. The 

 rock formation seen on the surface consists almost exclusively of a rather 

 dense finely grained sandstone, of light buff color on fresh fracture, but 

 weathering to a dull gray, a color effect which is also enhanced by the 

 covering of lichens on long exposed surfaces. In places the slope is covered 

 with loose angular fragments of this stone, ranging in size from hand speci- 

 mens to masses weighing several tons. These boulders piled upon each 

 other at all angles over many rods of the surface, as is often the case, pre- 

 sent a very curious appearance. They bear some resemblance to the coarser 

 material left by terminal morains in the glaciated regions. Or perhaps 

 they might better be compared to the packs of ice blocks that accumulate 

 in some northern rivers after the break up of the winter accumulation. 

 They probably owe their origin to the breaking down of layers of the 

 heavily bedded sandstone alternating with shale, which were tilted at a 

 high angle in the opposite direction to the slope of the mountain side. 

 As the softer shale weathered out more rapidly it left the layers of sand- 

 stone standing as a hanging wall, which under the combined effect of 

 gravity and erosion kept breaking off and shifting and sliding down the 



