306 THE PASSAGE OF COAL INTO DOLOMITE. [Aug. I9OI, 



interest, from its bearing on the origin of coal. His own obser- 

 vations of coal-seams in India had led him to question the origin of 

 those seams by growth in situ ; and though he held no fixed opinion 

 regarding this, he favoured what was known as the ' drift-theory.' He 

 feared, however, that the Author's paper would in future be quoted 

 as the strongest piece of evidence that had been produced in favour 

 of the growth-in- situ theory ; for while it was easy to understand 

 how a calcareous or other mineral deposit could be formed under 

 water in, or on the margins of, a forest or a bog, it was difficult to 

 understand how such easily transported debris as vegetable matter 

 could so abruptly cease and give way to a mineral deposit, as had 

 been described by the Author, if the coal had originated by sub- 

 aqueous deposition. The instances quoted by the previous speaker 

 did not appear to be strictly analogous, as they were cases of one 

 stratum thinning out and an adjacent one thickening, the two 

 retaining their distinctness; but if he correctly understood the paper, 

 in the condensed form as read, there was here not a thinning-out of 

 the coal and a thickening of the dolomite, but a transition in the 

 mineral character of the bed, which seemed more easily explicable 

 on the theory of growth in situ, than on the drift-theory of the 

 origin of coal. 



The Peesident also spoke. 



The AuTHOE, in reply to Mr. Hudleston, remarked that the 

 vegetable matter constituting a coal-seam differed from other 

 sediments in its capability of remaining longer in suspension. The 

 coal and the dolomite were most intimately connected ; for the 

 dolomite appeared first as thin streaks in the seam, and it was only 

 by the gradual expansion of these that the coal was finally replaced. 

 The Permian rocks were not developed in that part of the country, 

 and the New Red Sandstone rested directly upon the Coal-Measures. 

 With respect to dolomitic tufas, it seemed to him that the Magnesian 

 Limestone might itself be so described : it was difficult to see from 

 what source the dolomitization of that rock could have proceeded 

 subsequently to its formation . Several of the limestones described by 

 Mr. Gibson contained organisms, some of them in great abundance: 

 none had been found in the Wirral dolomite. So far the exploration 

 had disclosed a rock of fairly constant composition, but the dolomite 

 might be found to pass into an ironstone at any moment, in which 

 case the parallel with some of the Staffordshire rocks would be nearly 

 complete. On the drift-theory of the origin of eoal, referred to by 

 Mr. Oldham, it might be supposed that the dolomite was formed in 

 an area which even drifting vegetable matter failed to reach, owing 

 to stagnation in the water. There was no margin to the area com- 

 parable with the bank of a pond. It was true, as remarked by the 

 President, that there were many recognizable fragments of wood ; 

 their occurrence in unusual number might have been due to their 

 having floated beyond the limit reached by the thoroughly macerated 

 vegetable matter. The coaly seams in the rock showed no unusual 

 characters. 



