numerous, that formed a vast circle. We shall make for one of the most regular of this last class, viz., Eratosthenes. But, before reaching the foot of this range, we must pass over bright rays, radiating from the circular mountain, Copernicus. These rays are one of the most marked features of the moon, as seen through a telescope. Oken speaks of mountains as the organs of a planet, and, certainly, these mountains may not inaptly be represented by a star-fish with its diverging rays. But now we can examine the mystery, and we find that the rays are trap-dykes, rising little, if at all, above the level of the general surface. They appear as bright rays through the telescope, merely because they reflect the light better than the rest of the plain. No mould or verdure has covered them up, as the lava of Vesuvius has been by the vine-clad slopes. Not even does the lichen grow upon them, and hence they are clearly discernible from the earth. We can even discover where one dyke cuts another, and tell which is the older of the two. We can thus draw up a chronological scale for the convulsions of the moon. Some of the rays are evidently superficial streams of lava.
But let us pursue our journey onwards to our destination, Eratosthenes. This circular mountain, or rather range of mountains, is thirty-seven miles in diameter; and we know its dimensions more accurately than those of the mountains of our globe. The ascent is by a comparatively easy slope. We do not feel
