Planking

“ Then, taking the planks at each edge of the centre, by the same law their change and behavior will be quite different: they will still retain their original thickness at the centre, but will be a little reduced on each edge throughout, but the side next to the heart of the tree will be pulled round or bent convex, while the outside will be the reverse, or hollow, and the plank will be considerably narrower throughout its entire length, more especially on the surface of the hollow side. ”

“ Where the water falls over the rock, the oblique and curved lines used are broken, to represent the nature of the rock underneath. Notice that the depth of each little fall corresponds with the stratification of rock. The water, as it recedes, lies level, also. You will have no difficulty in drawing ponds and lakes, if you think of the farther shores as less distinct, and the waves, although rough and broken in the foreground, as merged and blended together in the distance. ”

“ In the first case, the experiments are made in or very near to mineral veins, which, by their character of filling fissures on lines of disruption, remind us of the general geological conditions of appearance of hot springs; the second set of experiments takes place in collieries and other excavations of like nature, among the stratified rocks, with or without dislocations. In each of these cases, either the temperature of the rock, of air, or of a constant subterranean spring may be tried. ”

“ On like an arrow sped the plank, straight for the centre of the opening, and all hope that it might drift against the weir was gone, when, suddenly, with a jar that almost flung me from my insecure perch, the front end of the plank struck something hidden below the muddy water, probably a sunken stake, and instantly was swung side on, jamming across the very mouth of the gates. Gathering all my few remaining energies, I made a feeble leap, and more by good luck than good management reached the top of the weir. ”

“ Physically plankton life must depend on this salinity and also on temperature, pressure, light, and movement.
(If plankton only inhabits surface waters, then density, temperatures, &c., of surface waters must be the important factors. Why should biologists strive for deeper layers? Why should not deep sea life be maintained by dead vegetable matter?) ”

“ I sought out a long flexible plank, and arranged eight tubs on it, close to each other, leaving a piece at each end to form a curve upwards, like the keel of a vessel. We then nailed them firmly to the plank, and to each other. ”

“ The rock mantle and its shield in the mat of vegetation.—Through the action of weathering, the rocks, as we have seen, lose their integrity within a surface layer, which, though it may be as much as a hundred feet or more in thickness, must still be accounted a mere film above the underlying bed rock. The mechanical agents of the breakdown operate only within a few feet of the surface, and the agents of rock decomposition, derived as they are from the atmosphere, become inert before they have descended to any considerable depth. ”

“ This substantial production of alternating poles upon the planet takes place through the diversity of its surface as water and land, through the oblique position of its axis, whereby summer and winter are produced, through the processes, or through the life that is upon it, through the processes of decomposition and combination effected by water, through the revival and death of vegetation, and even the white colour of snow. The planet discharges its pole in the neighbourhood of the sun, like a cork pellet, and reloads of itself at a distance from the sun ”

“ Both masses had well-defined “peaks,” and I came to the conclusion that the instruction to “draw a line from one black rock to the other” would mean that a straight line must be drawn, or ranged, from one of these well-defined peaks to the other. So I temporarily removed the telescope from my sextant, and, levelling it upon the extreme peak, or highest point of the rock I occupied, brought it to bear upon the corresponding peak of the other rock. ”

“ French nodded. This was certainly very satisfactory.
“Besides, sir,” Daw went on, “think of a plank laid as you’ve suggested and with the end of it partly sunk. It’ll not be easy to pull out, particularly when the ground you’re pulling from is not very firm. You won’t do it without leaving pretty deep footmarks, and the plank will leave a sort of trough where it was slid out. ”

“ And hence if the geologist would form an accurate conception of the origin and structure of many of the stratified rocks, he must study them not in hand specimens neatly trimmed and arranged along the shelves and drawers of a cabinet, nor even in the ponderous blocks daily exhumed by the quarryman, but along some surf-beaten cliff-line or down some precipitous ravine where the rock for centuries has been exposed to the wear and tear of the elements. ”

“ Here the science of geology takes its start with the metamorphic rocks, and it is the dividing line between the inner, smaller, and the outer, larger, planets.
IV. The Terraqueous Stage, when the surface has become substantially stable, there are great oceans gradually diminishing in size, and land gradually increasing. This is the stage of the sedimentary rocks, the time when the planet passes from its own supply of heat to dependence upon that of the sun; the stage when life begins, and the one in which the Earth is now. ”

“ To obtain a general idea of the nature and method of our science before beginning its study in detail, we may visit some valley, such as that illustrated in the frontispiece, on whose sides are rocky ledges. Here the rocks lie in horizontal layers. Although only their edges are exposed, we may infer that these layers run into the upland on either side and underlie the entire district; they are part of the foundation of solid rock which everywhere is found beneath the loose materials of the surface. ”

“ When beds of sand, clay, and marl, containing shells and vegetable matter, are found arranged in a similar manner in the interior of the earth, we ascribe to them a similar origin; and the more we examine their characters in minute detail, the more exact do we find the resemblance. Thus, for example, at various heights and depths in the earth, and often far from seas, lakes, and rivers, we meet with layers of rounded pebbles composed of flint, limestone, granite, or other rocks, resembling the shingles of a sea-beach or the gravel in a torrent’s bed. ”

“ I said, "while we hold to this theory, have the feeling of the otherwise helpless sinking man, who is cleaving to a plank that just bears him up even with the surface of the water. In the choice between the plank and destruction, the advantage is decidedly on the side of the plank." ”

“ The lateral pressure arising from the unequal expansion of rocks by heat may cause one mass lying in the same horizontal plane gradually to occupy a larger space, so as to press upon another rock, which, if flexible, may be squeezed into a bent and folded form. ”

“ In this class we may place the theory that the poles of the earth have changed their position. Independently of astronomical objections, there is good geological evidence that the poles of the earth must have been nearly in their present places from the dawn of life until now. From the Laurentian upward, those organic limestones which mark the areas where warm and shallow equatorial water was spreading over submerged continents are so disposed as to prove the permanence of the poles. ”

“ The next stage, under b b, is formed of straight planks about 4 feet long, 15 inches broad, and 2 inches thick. The third stage, under c c, is made, like the bottom, of trunks of trees hollowed out into its bilging form. The last stage, above c c, is formed also out of the trunks of trees, so that the moulding is of one piece with the plank. This work, difficult as it would be to an European with his iron tools, they perform without iron and with amazing dexterity. ”

“ When thus impressed with the slow rate at which the land is worn away through subaerial and littoral action, it is good, in order to appreciate the past duration of time, to consider, on the one hand, the masses of rock which have been removed over many extensive areas, and on the other hand the thickness of our sedimentary formations. ”

“ The fact that I compared the theory of selection to a plank on which a shipwrecked man seeks deliverance excited so much delight in the camp of the other side that they, in the pleasure of repeating it, made a straw of the plank. There is, however, a great difference between a plank and a straw. The man who is dependent on a straw sinks; a common plank has saved many a man's life. Thus the fourth difficulty is no longer transcendent when it is earnestly, thoughtfully met. ”

“ The effect of the distance of the surface of the solid rock from the under surface of productive soil may be both direct and indirect, and may vary much, not only with reference to the species of rock, but also to the vegetables. ”

“ The spring, after running about sixty feet, divides, and spreads itself over the top of the rock, whence it trickles very fast, from thirty or forty places, into a channel hollowed for the purpose, as seen in the cut, each drop producing a musical kind of tinkling, probably owing to the concavity of the rock, which, bending in a circular projection from the bottom to the top, occasions its brow to overhang about fifteen feet. ”

“ Thousands of cases are to be found in every group, of rocks and lines horizontal at the top of the mountain and vertical at the bottom; but they are still the exceptions, and the average out of a given number of lines in any rock formation whatsoever, will be found increasing in perpendicularity as they rise. ”

“ To give a Spherical Figure to a Plain by a Plain, (which at first sight may seem at Paradox) by moving one Plain upon another by a circular Motion, proceed to this manner: Let the piece to which the Glass to be wrought is fastned, be adjusted in the head of a Pole, which is to be of the length, the Semi-diameter of the Sphere of the Lens requireth; and, upon the Stool or Form, where you intend to work, let there be put a Plain of Iron or other Mettal, level to the Horizon; and perpendicularly over this Plain let the Pole be fasten'd to the Ceeling of the Room, if it be high enough ”

“ A peculiarity I have noticed in the soft, slaty ranges, is the very great inclination of the sides of ranges and gullies, having a good covering of soil, with grass and trees, and which I have seen considerably greater than that which geologists seem to have assigned as the extreme limit at which rock can carry a soil. ”

“ Thence it pursues its way to the head of the fall in a rough, solid rock channel, dashing on side angles, heaving in heavy surging masses against elbow knobs, and swirling and swashing in pot-holes without a moment’s rest. ”

“ But in place of sharp-rimmed escarpments, and tors, and broken shattered ridges, we see everywhere a rounded and smoothly-flowing configuration which prevails up to a height of 1600 feet or thereabout, above which the rocks take on the rugged appearance which is natural to them. By what magic have the strata at the lower levels escaped in such large measure from the action of rain and frost, which have furrowed and shattered the higher mountain-tops? ”

“ The manner in which the soil is influenced by a difference in the arrangement and position of the strata, will become evident, on comparing districts in which one particular sort of rock lies beneath the surface in horizontal strata, with others in which the solid substratum is composed of various rocks differing in their inclination towards the horizon. ”

“ Near the lithosphere surface the rocks support by their strength the load of rock above them, but at greater depths they are unable to do this, for the load bears upon each portion of the rock with a pressure equivalent to the weight of a rock column which extends upward to the surface. ”

“ The [109] springs do not gush out in streams as from rocky formations, but ooze up into great mounds, frequently involving an acre or more, like a great conical sponge, up the side of which you can walk, the water gushing out under every footstep, giving an impression that you may sink in all the way to the top, where you will find an open spring several feet across, the water from which seems to be absorbed by this spongy mound of earth and vegetation, so that a stream rarely runs away. ”

“ Be it that, in holding this theory, we experience the sensations of a man who as his only hope of rescue from drowning clambers on a plank which can only just keep him above the water: when the choice lies between a plank and drowning, the plank has a decided advantage. ”

“ Down farther, another projecting rock tears the water to pieces again and sends it shooting out into the air, till, when it reaches the bottom and has fallen a distance of fully seven hundred feet, there is scarcely anything left of the water but foam. ”

“ Mountain ranges observe a singular uniformity of direction, and the cleavage planes of rock are evidently determined by some all-pervading power. Mineral bodies are not distributed in all rocks indiscriminately. ”

“ For in a right sphere the needle is parallel to the plane of the horizon; but when the cœlestial pole is vertically overhead, or when the pole of the earth is itself the place of the region, then the needle is perpendicular to the horizon. ”