80 REPORT— 1869. 



this region, and it is a subject of interesting inquiry as to how this state of 

 things has been effected. Has the filling up, has the wearing down, if such 

 is the case, been gradual? and what forces have been concerned in producing 

 the mutilated forms we now observe ? " 



" Brightness and colour may ultimately become keys by means of which a 

 better acquaintance may be obtained with the chronological sequence of lunar 

 formations. Chacornac refers the great continental formations to an epoch 

 anterior to that of the production of the great plains, this, again, being anterior 

 to the period of explosive energy, contributing to the existence of numerous 

 objects, such as bowl-shaped craters and smaller blow-holes, within the 

 interior of which no intrusive matter is found. Reference, however, is not 

 prominently made to objects in mountainous regions similar to those which 

 we find in various portions of the great plains, viz. partly buried craters and 

 partially destroyed rings, of which we have evidence in this and adjoining 

 areas to the "W". The contrast of the general coloitr of the surface hereabout, 

 as compared with that of the grey plains, its mottled and rugged aspect, 

 arising probably from its altered character from that which it possessed at 

 a still earlier epoch, the absence of that sharpness of outhne in its remaining 

 mountain-peaks or ranges so characteristic of those which we find nearer to 

 and often on the grey plains, together testify to a much earlier epoch than 

 even that of the production of the partly filled rings on the grey plains. 

 Bright, white, glistening surfaces, more or less in the neighbourhood of 

 bowl-shaped craters,'and dark patches of deep grey approaching black, appear 

 alike to indicate the most recent formations — the first, it may be, from loose 

 fragmentary incoherent materials ejected from adjacent craters ; the last 

 from substances in a state at least of comparative fluidity, which have escaped 

 from the interior reservoii's at the times of eruption. Phillips compares the 

 bright glistening region o{ Aristarchits to one in which tvhife trachyte abounds ; 

 and many of the basalts in terrestrial volcanic regions present a dark colour. 

 Between the brightest and darkest of such limited areas on the moon's surface 

 every gradation of intermediate tint occurs ; and from a careful consideration 

 of the physical aspect of those regions which, on the one hand, reflect con- 

 siderably less light than the brighter, and on the other considerably more 

 than the darker, it may be inferred that such regions are amongst the most 

 ancient of lunar formations." 



A very ancient formation has been traced on area IV A"", the earliest state 

 of which is considered to have been very similar to many of the more recent 

 districts, such as those in which perfect craters and mountainous regions 

 intermingle. The first change which appears to have taken place on this 

 formation is that of the production of a grey plain, traces of which still exist. 

 The material of this plain appears to have invaded certain craters, breaking 

 down the walls of those immediately facing the plain, and partially filling 

 others. The next change appears to have been of an elevatory character, 

 the evidences consisting of a line of low mountains which has in a great 

 measure obhterated the characteristics of a grey plain and introduced those 

 more in accordance -with an ancient district, which are strikingly in contrast 

 with the features of the more recent craters to the E. The only instance of 

 volcanic outburst on this ancient district consists of a chain of craterlets of 

 quite an insignificant character. 



The determination of the successive changes before alluded to rests on the 

 strong indications, afforded by the careful study of photograms, of the priority 

 and posteriority of weU-marked features, which can only be realized by 

 contemplating the lunar picture in the seclusion of the study. "While the 



