50 Proceedings of the Royal Physical Society. 



Unfortunately, the solutions experimented on were too strong 

 for my experiments. I did try, however, if there was any 

 general agreement between the conductivity of the solution 

 and their power of sustaining clay. Potassium Sulphate was 

 the lest conductor, but it turned out, contrary to my expecta- 

 tion, that it kept the clay up longest. This may be explained 

 by the fact that the action of the Potassium as an alkali to 

 support the clay was scarcely overcome by the Sulphuric 

 Acid. Zinc Sulphate and Copper Sulphate may be supposed 

 a fairer comparison. Copper Sulphate is the better conductor 

 of the two, and I found it also cleared faster and very nearly 

 in the same proportion as its conductive power. In the whole 

 three, the rate of diminution of time of clearing corresponds 

 pretty well with the rate of increase of conductivity. 



These experiments, though very general and far from con- 

 clusive, still point hopefully in the direction I have indicated 

 for a solution of the problem. 



III. — Note on Fossil Corals from the Conglomerate of 

 HahUe's Howe, Pentland Hills. By Egbert Ethe- 

 RiDGE, Esq., Jun., F.G.S. Communicated by Charles 

 W. Peach, Esq., A.L.S. 



At a meeting of the Edinburgh Geological Society during 

 the last session, Mr John Henderson* read a paper on some 

 fossils obtained by Mr D. J. Brown and himself from the 

 conglomerate of Habbie's Howe. They consisted of a few 

 Brachiopoda and some fragmentary specimens of Corals, from 

 the rounded and semiangular limestone boulders and pebbles 

 contained in the upper part of the bed. 



The conglomerate unconformably overlies the Silurian 

 rocks of the Pentland hills, and is considered by Professor 

 Geikie to be of Old Eed Sandstone age. 



The pebbles enclosing the specimens consist of a dark- 

 coloured limestone, with numerous fragments of small encrinite 

 stems. The Corals, with one exception, belong to the Tabnlata, 

 the exception being a portion of a small Rugose Coral, in too 

 fragmentary a condition to be determined with certainty. 



* Transactions, II., pt. 3, p. 389. 



