684 REPORT— 1888. 



that ' the pfreat successive groups of stratiform crystalline rocks mark necessary 

 stages in the mineralogical evolution of the planet ' ; and that the principles which we 

 Lave elsewhere laid down will help us ' to recognise the existence and the necessity 

 of an orderly lithological development in time.' The reader who desires to follow 

 the questions here raised will find them discussed in the author's ' Mineral Physio- 

 logy and Physiography, (Boston, 1886), at much length in chapters V., VI., VII., 

 and VIII., and further noticed in the Appendix, p. G88, where will he found 

 references to previous pages here cited. 



2. Report on the Microscopic Structure of the Older EocJcs of Anglesey. 



See E.eport.s, p. 367. 



3. On a prohable Cause of Contortions of Strata. 

 Bij Charles Ricketts, M.D., F.G.S. 



The amount of compression to which the crust of the earth would be subjected 

 as the effect of subsidence, by the presence of faults and other causes, as well as by 

 the secular cooling of its mass (Rev. 0. Fisher, ' Phil. Mag.,' Jan. 1888), is too in- 

 considerable to develop the great contortions and foldings certain strata have 

 undergone. 



AVhen accompanied by cleavage, the distortion of contained fossils and the 

 displacement of included rock fragments (the flat sides lying parallel to the 

 cleavage planes), indicate that the change occurred whilst the clay deposits were 

 in an unconsolidated or plastic condition. 



It is suggested that these flexures may be dependent on irregular pressure, 

 caused by the local distribution of larger and heavier particles on accumulations of 

 unconsolidated muddy deposits, in a similar manner to what may be demonstrated 

 by spreading layers of clay of various colours, dried and reduced to powder, in a 

 trough ; when, on the admission of Avater, the clay has become plastic, sand is 

 heaped on some special part and extra weight applied, which in the experiment is 

 necessary. The heavier substance subsides into the plastic mass, and at the same 

 time the clay beds are squeezed outwards, causing the layers underneath to be 

 formed uito films, which are still continuous with those on the sides, though these 

 are rendered considerably thicker than in their original state and are curved into 

 folds, even to reversal of the beds, representing on a small scale what are frequently 

 met with in stratified rocks. The experiment so coincides with natural phenomena 

 that it is reasonable to expect it will prove to be a true and frequent cause of the 

 contortions of strata. 



4. On the Temperature at which Beryl is decolorised.^ 

 By J. Jolt, M.A., B.E. 



Experiments on some translucent green and yellow beryls from Glencullen, 

 Co. Dublin, show that these beryls are almost entirely deprived of colour when 

 exposed for one hour to a temperature of 357° C, i.e., the temperature of boiling 

 mercury at atmospheric pressure. The loss of colour takes place whether the 

 beryls are out of contact with the air or not. It was found further that exposure 

 to a temperature of 230° C. for the space of 30 hours effected a marked loss of colour. 

 In all cases the crystals retain their translucency. They have shown no signs of 

 regaining colour during a lapse of three years since the date of the experiments. 



The author suggests that this observation may bear on the history of the 

 containing granite subsequent to the formation of beryl if the colour of the latter 

 be regarded as indicating a major limit to the changes of temperature experienced 

 by the rock. 



' Proc. Royal Dublin Soc. vol. v. p. 51. 



