We alluded in Chap. III. to the phenomena of wrinkling or puckering as productive of certain mountainous formations; and we pointed out the striking similarity in character of configuration between a shrivelled skin and a terrestrial mountain region. We do not perceive upon the moon such a decided coincidence of appearances extending over any considerable portion of her surface; but there are numerous limited areas where we behold mountainous ridges which partake strongly of the wrinkle character; and in some cases it is difficult to decide whether the puckering agency or the exudative agency just discussed has produced the ridges. The district bordering upon Aristarchus and Herodotus, above referred to, is of this doubtful character; and a similar district is that contiguous to Triesnecker (Plate XI.) There are, however, abundant examples of less prominent lines of elevation, which may, with more probability, be ascribed to a veritable wrinkling or puckering action; they are found over nearly the whole lunar surface, some of them standing out in considerable relief, and some merely showing gentle lines of elevation, or giving the surface an undulating appearance. A close examination of our picture-map (Plate IV.) will reveal very numerous examples, especially in the south-east (right-hand-upper) quadrant. Some of these lines of tumescence are so slightly prominent that we may suppose them to have been caused by the action indicated by Fig. 6 (p. 28), while others, from their greater boldness, appear to indicate a formative action analogous to that represented by Fig. 9 (p. 29). [Illustration: IDEAL SKETCH OF PICO AS IT WOULD PROBABLY APPEAR IF SEEN BY A SPECTATOR LOCATED ON THE MOON.] [Illustration: PLATE XVII. WARGENTIN.] CHAPTER XI. CRACKS AND RADIATING STREAKS. We have hitherto confined our attention to those reactions of the moon’s molten interior upon its exterior which have been accompanied by considerable extrusions of sub-surface material in its molten or semi-solid condition. We now pass to the consideration of some phenomena resulting in part from that reaction and in part from other effects of cooling, which have been accompanied by comparatively little ejection or upflow of molten matter, and in some cases by none at all. Of such the most conspicuous examples are those bright streaks that are seen, under certain conditions of illumination, to radiate in various directions from single craters, and some of the individual radial branches of which extend from four to seven hundred miles in a great arc on the moon’s surface.