Thus interpreted, the Appalachian forms of to-day may be ascribed to three cycles of erosion: a nearly complete Mesozoic cycle, in which most of the previously folded and faulted mountain masses were reduced in Cretaceous time to a peneplain or lowland of small relief, surmounted, however, in the north-east and in the south-west by monadnocks of the most resistant rocks, standing singly or in groups; an incomplete Tertiary cycle, initiated by the moderate Tertiary upwarping of the Mesozoic peneplain, and of sufficient length to develop mature valleys in the more resistant rocks of the crystalline belt or in the horizontal strata of the plateau, and to develop late mature or old valleys in the weaker rocks of the stratified belt, where the harder strata were left standing up in ridges; and a brief post-Tertiary cycle, initiated by an uplift of moderate amount and in progress long enough only to erode narrow and relatively immature valleys.
Non-myelinate nerve fibres are as resistant to fatigue as are the myelinate.
Carbides of chromium are known; when the metal is heated in an electric furnace with excess of carbon, crystalline, C2Cr 3, is formed; this scratches quartz and topaz, and the crystals are very resistant to the action of acids; CCr 4 has also been described (H.
This, of course, naturally leads to the production of a wine somewhat different in character to that produced before the epidemic, but this difficulty may be overcome to some extent, as it was in the Bordeaux vineyards, by grafting ancient stock on the roots of new and resistant vines.
More indirect methods, such as the grafting of less resistant scions on more vigorous stocks, of raising special late or early varieties by crossing or selection, and so on, have also met with success; but it must be understood that resistant in such cases usually means that some peculiarity of quick growth, early ripening or other life-feature in the plant is for the time being taken advantage of.
But in the derivant valley peneplains developed in the present cycle of denudation, and there are residual summits also; in the Connecticut Valley trap ridges, of which Mt Tom and Mt Holyoke are the best examples; at Mt Holyoke, lava necks; occasionally in the lowlands, ridges of resistant sandstone, like Deerfield Mountain near Northampton; in the Berkshire Valley, summits of resistant schists, like Greylock, the highest summit in the state.
Thus he says that the silver which has been changed into gold by the projection of the red elixir is not rendered resistant to the agents which affect silver but not gold, and Albertus Magnus in his De Mineralibus - the De Alchemia attributed to him is spurious - states that alchemy cannot change species but merely imitates them - for instance, colours a metal white to make it resemble silver or yellow to give it the appearance of gold.
The results of the first cycle of erosion are seen in the widespread exposure of the resistant Carboniferous limestone as a broad platform in the south-western area of greater uplift through central Arizona, where the higher formations were worn away; and in the development of a series of huge, south-facing, retreating escarpments of irregular outline on the edges of the higher formations farther north.
Many remedies for this disease have been suggested, including total submersion of the vineyards, the use of carbon bisulphide for spraying, and of copper salts, but there appears to be little doubt that a really serious epidemic can only be dealt with by systematic destruction of the vines, followed by replanting with resistant varieties.
Each escarpment stands forth where a resistant formation overlies a weaker one; each escarpment is separated from the next higher one by a broad step of weaker strata.