1880.] a7id vegetable matter hy conferva. 341 



As the plant during its period of hibernation lies at the bottom 

 and some of the fine sediment which is carried by the rains into 

 the lake must settle on it, it seems hardly possible that it could 

 disengage itself from the mud in the summer without lifting some 

 with it from the bottom, though it must clearly be only a very 

 small quantity of the very finest. This point however I have not 

 yet been able to verify by obtaining some of the water when the 

 plant was beginning to rise, and it cannot be observed in the same 

 way as in the case of the coarser confer void growths. 



But it seems most probable that by this also among the small 

 but ceaseless operations of nature the mud is being unsettled, lifted 

 and drifted now further out, now nearer shore, to be left at rest 

 only when it has dropped into water too deep, or on a spot other- 

 wise unsuitable for the plants which help to transport it. 



(2) Professor T. M'^K. Hughes. On the altered rocks of 

 Anglesea. 



In 1820, Professor Henslow made a careful collection of the 

 rocks of the island and gave a description of them and their mode 

 of occurrence in an excellent paper published in the Transactions 

 of this Society \ This collection is in the Woodwardian Museum. 



Professor Sedgwick worked over the district, but has only 

 referred to it here and there in his published Memoirs. From 

 his MS. notes, however, we learn that he generally agreed with 

 Henslow's identifications. 



Professor Ramsay has described the district, in detail in the 

 Maps^, Sections^, and Memoir* of the Geological Survey. I find 

 myself obliged to return much nearer to his views in some cases 

 where the opinions of subsequent writers^ had prepared me for 

 a different interpretation, and I would refer the principal schistose 

 masses to altered Cambrian and Silurian, though to a different 

 part of the series from that to which he would assign it, and 

 though I generally offer a different explanation of the nature of 

 the change that has taken place. 



The definition of metamorphism is beset with difficulties, for 

 few rocks have retained the character they had when first formed, 

 and the most extreme alteration and replacement does not seem 

 to be connected with the greatest changes of temperature as in- 

 ferred from other evidence. 



It is quite common in examining folded rocks to find that a 

 shale has been rolled out as it were at the expense of its thickness, 

 so as in its undulations or crumples to cover a much larger super- 

 ficial extent than it did originally. One proof of this is that when 



1 Tram. Phil. Soc. 1821. 2 Sheets 75, 78. 



3 Sheet 40. * 3Iem. Geol. Surv. Vol. in. 



" Hicks, Q. J. G. S. Vol. xsxv. p. 296. Callaway, Q. J. G. S. Vol. xxxvi. p. 2. 



