156 Mr Hicks, On some Irregularities in ike Values [May 26, 



materials constituting the original beds. For II. and IV. are in 

 parts so highly crystalline that they begin to resemble an igneous 

 rock, while III. has no such resemblance, nor yet I. ; while V. is very 

 markedly sedimentary. Thus we have two extremely crystalline 

 series intercalated between others far less so. The difference in 

 character cannot be due therefore to any such cause as one series 

 having been subjected to a greater central heat than another, or to 

 contact metamorphism, or to heat developed in compression. The 

 dykes, which are numerous, penetrate all alike. The neighbouring 

 granite is equally remote from all. The compression must have 

 operated equally on all. Thus the only explanation for the dis- 

 tinctness of these several series seems original difference of 

 constitution. 



In a paper recently published by Mr Marr he suggests the 

 subaerial and volcanic origin of Archaean rocks. The facts which 

 I have noticed agree pretty well with subaerial origin. The 

 general arrangement of the constituents rather into lenticular 

 masses than laminae, the occasional larger lenticular masses or 

 short seams, and the frequent appearances of false-bedding, where 

 the bedding is sufficiently distinct, all point in that direction. So 

 perhaps may the frequent and well-marked nodes or patches, which 

 abound in the highly crystalline Series II. and exactly resemble 

 those so common in granites. 



But in favour of the volcanic origin I have no facts to adduce. 

 I have seen no indications of agglomeratic constitution nor of 

 included fragments. And I think some such might be expected. 

 I am more inclined to go back to the older hypothesis, and imagine 

 that the Archaean rocks took their origin when the surface of the 

 earth was in some respects exposed to different conditions than 

 those which we now experience. 



May 26, 1884. 

 Mr Glaisher, President, in the chair. 



Prof. E. Ray Lankester was elected an honorary member. 

 S. L. Hart, M.A., St John's College, was elected a Fellow. 



The following communications w T ere made : 



(1) On some Irregularities in the Values of the Mean Density 

 of the Earth, as determined by Baily. By W. M. Hicks. 



I have recently been examining Baily's observations on the 

 mean density of the earth in order to see if they showed any traces 

 of a dependence of the attraction between two masses on their 



