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Proceedings of tlie Royal Society of Edinburgh. [Sess. 
the crushing teeth of fishes. Such compound corals as Lithostrotion and 
Lonsdaleia occur in regular bands in the position in which they grew, or 
in nests associated with brachiopods, gasteropods, polyzoa, etc. These 
limestones appear to have been formed of the detritus of calcareous 
organisms laid down beyond the reach of terrigenous sediments. 
When we reach the top of the Blackbyre Limestone we find that the 
character of the limestones undergoes a sudden change, showing that the 
clear water coastal conditions under which the lower limestones were 
deposited had been replaced by an upheaval of the sea bottom, so that 
when the land again began to sink below the level of the sea, estuarine 
and lagoon conditions prevailed, in which river-borne mud derived from 
the land was being deposited. The succeeding limestones from the Hurlet 
Limestone up to the Top Marine Limestone indicate that the physical 
conditions prevailing over Central Scotland during their deposition were 
of a fairly uniform character compared with those which existed before 
the deposition of the Hurlet Limestone. 
XVI. Summary of Conclusions. 
The main object, then, of this paper has been to show that the different 
calcareous horizons in the Hurlet Sequence from the Hollybush Limestone 
up to the Top Marine Band can be traced right across Central Scotland to 
the East Coast. In the neighbourhood of Edinburgh the Hollybush and 
Blackbyre Limestones appear to be absent or at least are not typically 
developed owing to the existence over that area of estuarine conditions 
under which the oil shales were accumulated. But the occurrence of the 
Baldernock Limestone in its typical freshwater or estuarine aspect, the 
Hurlet Coal, and above all the Hurlet Alum Shale with its characteristic 
bone bed and lamellibranch and brachiopod faunas, present such a 
strong combination of stratigraphical and palaeontological evidence as to 
leave no doubt in our mind that we are here on the position of the Hurlet 
Limestone and its associated strata, and that the Hurlet datum line can 
now be definitely fixed on clear stratigraphical and palaeontological 
evidence. It has also been shown that the succeeding limestones, namely, 
the Blackhall, the Main Hosie, the Top Hosie or Calderwood Cement, and 
the Top Marine Limestone, can be identified over the whole of the area 
under consideration, not only on evidence of a purely lithological and 
stratigraphical character, but also by the fact that these different 
horizons present certain faunal assemblages which are sufficiently 
characteristic of the beds in which they occur to enable us to trace 
them over wide districts with a considerable degree of certainty. 
