the Bolton Bailway^ at Dixon Fold, near Manchester. 163 



being at least twice as broad as the aperture, the introduced 

 matter having a wider area to cover, would necessarily be 

 thinner and more diffused than its equivalent above. This 

 will also expUin the difference in the thickness of the shale- 

 band in and above the tree, which has been already alluded 

 to ; but here there is an additional cause. In the tree it is 

 nine or ten inches measured perpendicular to the plane of its 

 surface ; but above, where it is fifteen inches, the measure- 

 ment is taken on the slope of the excavation, which inclines 

 about 36° towards the railway, and as the strata dip about 

 17° in a contrary direction, it follows that in the section the 

 band will appear to be nearly one-third- thicker than that in 

 tlie tree. Again, no sediment from the water that was leloiv 

 the top of the tree could be admitted into it, which would 

 tend still farther to diminish the thickness of the lower band. 

 It is also necessary to bear in mind that when this shale-band 

 was formed, the top of the cylinder must have extended up- 

 wards of seven or eight feet higher than it does at present. But, 

 on this assumption, another apparent discrepancy will arise, on 

 comparing the relative thickness of the sandstone above the 

 shale-band, within and above the tree. Its present thickness 

 in the trunk is five feet six inches, and if to this we add about 

 seven feet six inches to its probable top at the time the pro- 

 cess was going on, it will exceed that of its supposed equiva- 

 lent above. But I think this only proves that when the sur- 

 rounding sediment had risen as high as the top of the cylinder, 

 a good deal of what afterwards settled round it would find its 

 way into the aperture in addition to that derived from the 

 water immediately/ above it ; the specific gravity of the sandy 

 deposit would cause it to slip down and form a quaquaversal 

 slope or funnel round the orifice, which, as the sediment ac- 

 cumulated, would collect it from a continually widening area, 

 and rapidly fill up the cavity.* Taking this and several minor 

 considerations into account, it seems probable that the tree 



* No indication of sudi an arrangement can be seen in the present in- 

 stance, because the top of the trunk and its suiTOunding matrix, for six feet 

 in every direction, have been removed in excavating for the railway ; but I 

 mention it that observation may bo directed to this point on any future die* 

 covery of fossil trees. 



