The Lunar Apennines. 381 



our choice of an explanation plastic enough to be moulded to 

 the varying and capricious nature of the phenomenon ; but 

 there is an embarras de richesses : the number of alternatives 

 causes difficulty in selection ; and after all, it is not wonderful 

 that we should be perplexed by an appearance which we are 

 obliged to study at a distance, which the highest available 

 magnifying powers can only reduce to 200 or 300 miles. What 

 would be the difficulties and the perplexity of the geologist if 

 he were obliged to study the structure of the earth from a cor- 

 responding remoteness, and in equal ignorance of its materials, 

 the processes to which they have been subjected, and — save 

 only in very rude outline — the causes and mode of their pre- 

 sent conformation ! However, this subject of varying reflective 

 power or local colour deserves, and we may hope will some day 

 receive, a greater amount of separate investigation than has yet 

 been accorded to it. 



11 Almost numberless," say B. and M., "is the multitude 

 of mountain ridges, separate peaks, and hills which cover the 

 highland ; and even with the strongest telescopic aid and the 

 most invincible application, a delineation, entering as much 

 into detail as is practicable, for instance, in the great maria, 

 would here be unsuccessful." They say that their map con- 

 tains on the W. of the crater Gonon, that is to say, in about \ 

 of the whole length of the chain, towards 500 summits, but 

 that 2000 or 3000 would not have been enough to exhibit all 

 which can by degrees be made out here under favour- 

 able circumstances. {( A three times larger scale, a gigantic 

 telescope, and the special examination of years, would be 

 requisite to produce a representation approaching in accuracy 

 to one of our better terrestrial maps." 



This complexity of structure had been noticed by Schr., 

 whose 27f. reflector, with a power of 200, had shown him in 

 1795-6 the innumerable minor elevations of which the great 

 masses are compacted together, in, so to speak, tangible dis- 

 tinctness, though in part as minute as the smallest pins' heads ; 

 the labyrinth, in fact, is not difficult to be perceived ; and I 

 have seen something of it with a 3 T V inch object-glass. 



Beginning on the S.W. from the end of Mt. Hcemus, which 

 forms the S.E. border of the M. Serenitatis, we come first to 

 the gradual ascent of a wide- spread platean, 180 miles from 

 N. to S., and 165 in the opposite direction ; an extent of 

 which we may get an idea by comparing it with the distance 

 from London to York, between 170 and 180 miles direct. 

 The general elevation of this mass may be perhaps 6000f., 

 much greater than the subsequent rise of the summits, which 

 it bears. The arrangement of most of these shows one of the 

 peculiar parallelisms of the moon, from N.E. to S.W. : one 



