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W. HUMBOLDT. Though close to the limb, this enormous wall-surrounded plain, some 130 miles in extreme length, and estimated to have an area of 12,000 square miles, is well worth observing under suitable conditions. It ranks among the largest formations of its class, and in many respects resembles Bailly on the S.E. limb.
It is about 40 miles in diameter, and has a somewhat irregular border, both as regards shape and height, rising at one peak on the S.W. to nearly 14,000 feet above a level interior, which apparently contains no conspicuous features. EAST LONGITUDE 60 deg. TO 90 deg. GRIMALDI. This ranks among the largest wall-surrounded plains on the moon, and is perhaps the darkest.
LACROIX. A ring-plain 20 miles in diameter, N. of Schickard. It has a prominent central mountain. SCHICKARD. One of the largest wall-surrounded plains on the visible surface of the moon, extending about 134 miles from N. to S., and about the same from E. to W., enclosing a nearly level area, abounding in detail.
Others, again, of considerable area, as, for example, the Mare Serenitatis and the Mare Imbrium, are bounded more or less completely by curved borders, consisting of towering mountain ranges, descending with a very steep escarpment to their surface: thus in form and other characteristics they resemble immense wall-surrounded plains.
It is, however, never sufficiently well placed for observation. BAILLY. One of the largest wall-surrounded plains on the moon, almost a "sea" in miniature, extending 150 miles from N. to S., and fully as much from W. to E. When caught at a favourable phase, it is, despite its position, especially worthy of scrutiny. The rampart on the W., of the linear type, is broken by several bright craters.
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