304 ME. A. STKAHAN OX THE PASSAGE OF A [Aug. I9OI, 



The insoluble residue of E 3270 contained: — 



Per cent 



SiO, 51-6 



TiO; 1-0 



AI2O3 S5-5 



Fe^Og 3-2 



91- 



Alkalies and small quantities of lime and magnesia not estimated. 

 The insoluble residue of E 3344-45 contained silica, iron, alumina, and lime. 

 Sufficient material was not available for quantitatiTC estimation. 

 The ignited insoluble residue of E 3280 was composed of: — 



Per cent. 



SiOg 64-50 



TiO, 1-24 



Al.,03 26-27 



FeA 2-32, ^QQ.g. 



CaO 0-62 > ^^^^^ 



MgO 0-89 



K,0 4-41 



Nap+trace of Li^O ... 0-39; 



The ratios of iron, lime, magnesia, and carbon -dioxide in the soluble portions 

 of the three specimens are : — 



CaO. FeO. MgO. CO,. 



E3280 1 -08 -92 197 



E3270 1 -02 -96 197 



E 3344-45 1 -17 '74 1-86 



EXPLANATION OF PLATE XII. 



Fig. 1. E 3270 X lU- Spherulitic dolomite. 



2. E 3280 xl2|-. Irregular layers of dolomite, with patches of mud. 



3. E 3279 X 12|-. Films of coaly matter ramifying through dolo)nite. 



4. E 3281 X 12^. Similar to tlie preceding, but with a fragment of wood . 



5. E 3344 X IO5. Woody tissue impregnated with, and cemented together 



by, dolomite. 



DlSCFSSIOK". 



Mr. HuDLESTON complimented the Author on the very graphic 

 description that he had given of a phenomenon, which, fortunately for 

 the interests of coal-owners in general, is said to be without parallel 

 in our islands. Accepting the facts as detailed by the Author, the 

 question of the causes leading to this singular passage of coal into 

 dolomite is certainly one of considerable difficulty. He (the speaker) 

 could remember the time when the origin of coal-seams was gener- 

 ally held to be due to vegetable growth in situ, each seam having 

 its appropriate underclay : persons holding contrary opinions did 

 not meet with much favour at the Geological Society. Undoubtedly, 

 the origin of coal-seams need not have been the same in all cases. 

 In this case the Author had adopted the view that coal is due to 

 sedimentation, where particles of organic origin play the part of 

 mineral clastic materials, such as make up the sands and clays of the 

 Coal-Measures ; and he was disposed to regard the failure in the 

 supply of this clastic material of vegetable origin as the cause of a 

 void which had been filled up by contemporaneous tufaceous deposits. 

 Herein lay the great difficulty : how were we to account for the 



