58 Proceedings of the Royal Physical Society. 



even though the search for them has been zealously pursued 

 for well on to half a century. 



It may, of course, be urged that the comparison between 

 the faunas of the Lower Carboniferous and Jurassic Rocks 

 on the one hand, with the graptolite fauna of the Proterozoic 

 mudstones on the other, is not a just one, seeing that the 

 terms of comparison are unlike in all three cases. While 

 admitting that to be true, the comparison in other respects 

 is useful in the present connection. 



In the Lower Carboniferous Rocks, as developed around 

 Edinburgh, eight or nine thousand feet of strata, which have 

 been formed under frequent changes of conditions, show 

 hardly any evidence of changes in their organic contents from 

 bottom to top. Whatever geographical changes occurred, 

 it is clear that they must have been of such a nature as to 

 leave no impress upon the organisms then living, in either 

 their embryonic or their adult stages of existence. The 

 Jurassic Rocks appear to have been formed under almost 

 identical conditions as these last — or, at any rate, the same 

 rapid changes from calcareous to either arenaceous or argil- 

 laceous types of sediment are of common occurrence in both, 

 as are also the repeated alternations of rocks formed in the 

 deep water of the sea with those deposited in one or other of 

 the estuarine and shallow-water conditions of a delta. But 

 there is hardly a platform in these rocks that does not con- 

 tain some distinctive or zonal fossil. Why should this be 

 the case in the Jurassic Rocks, and not the case in the 

 Carboniferous ? 



The now well-known case of the Graptoliiic Mudstones of 

 the Moffat area presents even greater difficulties of the same 

 kind as these just noticed. Near Moffat there is to be seen 

 a group consisting chiefly of dark- coloured mudstones and 

 shales, which have long been celebrated as affording most 

 excellent and well-preserved examples of a great variety of 

 graptolites, which, by the way, are very rarely accompanied 

 by fossils of any other kinds. The total thickness of these 

 graptolitic mudstones is a trifle under 200 feet. By means 

 of the fossils they contain, these strata can be paralleled with 

 sedimentary (or other) rocks of quite different character, and 



