SHELL-BEDS IN BRITISH COLUMBIA. 281 



recent deposit, which were already beginning to crumble under the 

 influence of the sun and the weather ; and at first I had serious 

 doubts whether such specimens might not in some way have worked 

 down into the bed from above; but I soon saw that this was 

 quite impossible, and, moreover, that most of the species were not 

 represented in the newer deposit. As the shells dried, this " bloom " 

 passed off, and they faded into rather brittle fossils. 



This remarkable state of preservation, which was most marked in 

 the seams where the shells were most abundant, was confined to 

 beds which lay some depth below the surface. Upwards the shells 

 became scarcer and more weathered, and they finalty disappeared 

 about 10 feet from the surface, so that in the upper portions of the 

 deeper sections there was not a trace of them to be seen. I could 

 not quite decide whether their absence in these cases was entirely 

 due to the decay of the shells, or whether they had never really 

 been present in the topmost layers of the Boulder-clay. There is 

 some reason for entertaining the latter view, for in the section 

 across the entrance to the dock, though, as already mentioned, no 

 shells were to be found in the Boulder-clay, their former pre- 

 sence was clearly demonstrated by their empty casts in the clay ; 

 whereas in the higher sections no similar casts could be found. It 

 is possible, however, that in this case casts may also at one time 

 have existed, but have been gradually filled in and obliterated by 

 the weathering of the clay and the percolation of muddy waters. 



Dr. Dawson has pointed out the reason for the great difference 

 in the condition of the shells, in one of the passages quoted at the 

 commencement of this paper. The thick forest-growth which has 

 for ages clothed almost every foot of dry land over the whole of the 

 island has accumulated a variable but persistent layer of vegetable 

 soil which has yielded solvents to the waters passing through into 

 the clays beneath, so that wherever there has been a circulation of 

 surface-water through the drifts, the shells and also many of the 

 smaller boulders of felspathic rocks have been softened and 

 crumbled or altogether removed ; but where the clays below the 

 surface have stood lower than the sea-level, they have been below 

 saturation-line, and there has consequently been little or no perco- 

 lation through them. The low-level section near the dock- 

 entrance is a seeming exception ; but in it the clays are at the 

 surface, though below sea-level, and it is probable that there has 

 been a slow passage of waters through the upper few feet of the 

 clay, while the decaying matter in the mud of a sea-bottom crowded 

 with life would no doubt furnish acids enough to destroy the 

 shells. 



It would be difficult to find a clearer demonstration of the intense 

 effect of slightly varying conditions on the preservation of organic 

 remains, nor a more striking illustration of the manner in which 

 beds have been denuded of their fossils, than is yielded by these 

 sections ; for here might be found, within the space of a few yards, 

 shells so fresh that it would have been easy to believe that the 

 mollusk was still within, others so soft ^ud decayed that they 



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