Geological Society of London. 375 



talline constituents in clay-slates, and at the outset he describes in 

 detail the microscopical character of clay-slate, of novaculite or 

 whetstone, and of carbonaceous shales and slates respectively, dwell- 

 ing more especially on the crystallized minerals which can be de- 

 tected in each of these rocks, and the nature of the isotropic ground- 

 mass which sometimes surrounds them. He then points out that 

 three theories have been advanced to account for the presence of 

 these crystalline constituents in clay-slates. According to the first 

 of these theories, the crystals in question are regarded as the product 

 of chemical action in the ocean in which the original material was 

 deposited. The second theory attributes the fonnation of the crys- 

 talline minerals to processes of metamorphism which have taken 

 place subsequently to the solidification of the rocks. The third 

 theory refers them to aggregative action going on in the still plastic 

 clay-slate mud prior to its solidification. The first of these theories 

 has been maintained by G. R. Credner, but against it the author 

 adduces numerous arguments, and especially points out the difficulty 

 of supposing an ocean capable of depositing from its waters at suc- 

 cessive periods minerals of such different chemical composition as 

 chlorite, actinolite, etc. In opposition to the second theory, which 

 has received the support of Delesse, the author points out the 

 existence in the rocks in question of broken crystals, which have 

 ■ been recemented by the surrounding clay-slate substance. The 

 author is thus led to incline towards the third theory, in favour of 

 which some striking facts, drawn from the microscopical structure 

 of the rocks, have already been adduced by Zirkel. He admits, how- 

 ever, that later metamorphic actions are not to be excluded in 

 seeking to account for the origin of the crystalline constituents of 

 clay-slates, and points out that four distinct stages must be con- 

 sidered in the series of changes by which the rocks in question have 

 acquired their present character : — 1 st, the deposition of the mud ; 

 2nd, the formation of minerals during the plastic state ; 3rd, the 

 separation of materials during solidification ; and 4th, the action of 

 metamorphic processes. 



6. " On a Section through Glazebrook Moss, Lancashire." By T. 

 Mellard Eeade, Esq., F.G.S. 



The section described has been exposed in a cutting made by the 

 Wigan Junction Railway. The moss rests on an almost perfectly 

 level floor of Boulder-clay, and is at the deepest part about 18 feet 

 thick. In the 3 or 4 feet at the base are branches, etc., of trees, and 

 the stools are found resting on and rooted in the Boulder-clay ; 

 these are of oak or birch. Prostrate trunks were found, one, an 

 oak, being 46 feet long and 3 in diametei*. The surface of the clay 

 is about 60 feet above O.D. The author thinks the section shows 

 that the moss originated from the decay of the forest, favoured by 

 change of climate, and gradually extended itself from the centre 

 outwards, trees within it at the outer part being much less dis- 

 coloured than those further in. In the latter part of the paper some 

 cuttings and borings in the clays and sands are described, and the 

 asserted occurrence of the trunk of a tree in the Boulder-clay is noticed. 



7. "On the Tertiary Deposits on the Solimoes and Javary Rivers 



