294 



THE GEOLOGIST. 



the land must have been depressed, and then the deposit became covered 

 over, in some places, with drifted mud and sand and gravel, so as to re- 

 present precisely the circumstances under which the trees were found at 

 Bolton. If similar submergences took place in tropic seas, coral reefs 

 would form over the peat and trees, and thus account for the occurrence 

 of limestone, as well as sandstone, shale and conglomerate, over the coal. 

 The formation of coal might be accounted for in various ways, and there 

 could be no doubt that drifted materials did form thin beds of coal under 

 precisely the same conditions, the vegetables being drifted so unmixed 

 with detrital matter, as to form a purely vegetable deposit ; but under 

 coal seams thus formed, there were no under clays with Stigmarise. He, 

 therefore, regarded the question of drift only as one of amount: if the 

 drift of vegetable matter was large, a bed of coal might result ; but he 

 had never seen a worlcable coal bed which did not hear out Mr. Binney's 

 conclusions. 



Mr. Philips remarked, that in the Lancashire coal-field there were only 

 about eighty-five beds of coal associated with a thousand beds of sand- 

 stone and shale, which had been unquestionably drifted by water, but 

 whether in a river, estuary, or deeper water, there were no data to deter- 

 mine. The evidence derived from the occurrence of trees in situ at St. 

 Etienne, as originally adduced by Brongniart, was not very conclusive, 

 from the various positions of the trees, and their fragmentary aspect ; 

 but this argument derived great confirmation from the trees at Dixon- 

 field, which were all at right angles to the plane of the coal-bed on 

 which they rested : a position in which drifting by water could not be 

 expected to place trees of different species, and possessing roots with 

 different structure, with so much regularity. It had occurred to him 

 that the abundance of cones at the base of the trees was also opposed to 

 the idea of drifting, as it would require different forces of water to drift 

 large trees and cones. The third class of phenomena was the occurrence 

 of shells and fishes, associated with and forming extensive layers over 

 the coal seams ; many of these shells were analogous to those living at 

 the present day in fresh waters ; the upper strata especially appeared to 

 be of fresh water origin. From all these facts, Mr. Philips stated, a 

 certain limited inference might be drawn; but he thought it was far 

 more important to establish a strict and logical process of reasoning, 

 to be employed in future investigations, than to arrive at any positive 

 conclusion in the present case. 



Mr. Sedgwick admitted, that the occurrence of trees in situ had been 



