61 



selves from the muddy deposit settling from the turbid water as its 

 tidal flow abated. 



Another reason why we might anticipate the burial of marine ani- Dying marine 

 mals on the ebb tide, is that those which had nearly reached the limit be buried on 

 of their life, would be revived when bathed in the fresh sea-current of tneebb - tide - 

 the flood-tide, coming to them charged with an abundance of food ; 

 whereas they would be more likely to succumb in the turbid returning 

 waters of the ebb-tide, which had been robbed of their nourishment 

 by other animals of the Benthos. Hence from these two causes, it is 

 probable the majority of the burials of marine animals in estuarine mud 

 will occur on ebb-tide, and we may look for the orientation of the 

 valves of animals that hung by a byssus or pedicle in the direction of 

 the ebb-tide. In fact this may be seen on any sandy shore where a few 

 stones serve to give a foothold for mussels. Another cause which 

 would help to the same result would be the undertow resulting from 

 the wave impulse from the ocean sweeping up into an open bay. The 

 translation of water near the surface resulting from the impulse of 

 these waves would have a complementary under-tow outward along 

 the bottom of the bay. 



Supposing the burial of the Etcheminian organisms to have occurred 

 at the time of ebb in a hypothetical estuary, occupying the Cambrian 

 valley of Indian, brook, the orientation of these organisms would im- 

 ply that the estuary opened to the north-east and that its head was to 

 the south-west, since the fossils are oriented to the north-east. But 

 such a hypothesis is not supported by the actual condition of the 

 Etcheminian sediment. For if the mouth of the estuary were to the 

 north-east, it would be natural to look for a greater thickness of 

 deposits in that direction, but the reverse is the case ; for while on 

 the Gillis branch of Indian brook the thickness of the Etcheminian 

 terrane is considerably less than two hundred feet, on Dugald brook, 

 two and a half miles to the south-west, it is five hundred feet, and at 

 Boundary brook, two miles further south-west, it is five- hundred and 

 fifty feet. 



These conditions imply that the mouth of an estuary in Indian 

 Brook valley, if such existed in Cambrian times, was to the south- 

 west and the orientation of the fossils should have been in that 

 direction, and not to the north-east, the actual direction. 



We therefore turn to the marine current theory as the more pro- A shore cur- 

 bable explanation of the orientation of the Etcheminian brachiopods probabfecmwe 

 of this valley. To give passage to such a current, we must suppose of orientation, 

 that the neck which now connects Indian brook valley with that of 



