SONNINIA— SUMMARY. 455 



off the spatulate auricles from tbe termination of the species called " Ammonites 

 Braihenridgii " would cause no harm to the thickened, arched aperture of 

 " Am. Humphriesianus," wholly unprovided with any projections. However, 

 many beds of Ammonites are remarkable for the extremely perfect preservation of 

 the specimens with their delicate mouth-processes intact ; in fact, the loss of the 

 process is, in these cases, an accident accompanying extraction, and not an 

 accident that happened before fossilisation. It is arguable that, in beds where 

 Ammonites are so perfectly preserved, the specimens found have not been exposed 

 to the accidents of dispersal, and that they were fossilised on the spot where they 

 lived. This does not say but that many of the shells which did live on that spot 

 may, owing to various causes, have been dispersed, and have been thrown on the 

 nearest coast. 



In regard to coastal deposits, it may be remarked that though many shells 

 might be cast on a beach at different times, yet, except in certain cases, these 

 shells would not form a deposit there — not a fossiliferous deposit, because many 

 causes would combine to break the shells into fragments, and the result would 

 generally be the formation of a shelly sandstone. Therefore the finding of shells 

 of Nautilus and Spirula on coasts at the present day is not necessarily evidence 

 that in those places fossiliferous deposits yielding Nautilus and Spirula will be 

 found in the future. The evidence of a coastal deposit is not difficult to recognise ; 

 but Ammonitiferous beds do not seem to yield it. Therefore if the Ammonites 

 which are found in the rocks have been dispersed from where they lived, they have 

 been stopped on their journey, and have not reached the shore. The argument is, 

 that if they reached the coast, little or nothing, except fragments, would generally 

 be left to tell the tale after a few months ; but that if they were preserved under 

 certain circumstances in a coastal deposit there would be other evidence showing 

 that it was such a deposit. 



This much can certainly be said as regards the place where Ammonites were 

 fossilised. It was sometimes, if not the more frequently, in places where there 

 was little sediment being collected ; in certain cases it was where Ostrese, Serpulae, 

 and small Brachiopoda could attach themselves to the dead shells and grow, and 

 where various organisms could bore them ; also the process of fossilisation went 

 on in comparatively shallow water, — that is, probably well within the 100-fathom 

 line, 1 and in comparatively narrow seas, sometimes almost land-locked bays, but 



1 Presumably, in the case of Dorset, Ammonites were fossilised in abundance during Inferior 

 Oolite times at distances between twenty and fifty miles from the supposed land. In Gloucestershire 

 the distance was from less than fifteen miles ; in both these cases the preservation of the specimens is 

 on the whole remarkable — the delicate mouth-processes being preserved. On the other hand, in the 

 case of clays — presumably deep water deposits — it may be noticed that in them, or even in the 

 limestone bands they contain, the Ammonites, though fairly preserved on the whole, are usually 

 deprived of mouth-processes, and even of all their body-chamber. 



