No. 4.] BILLINGS — ON THE TACONIC CONTROVERSY. 463 



•' Without knowing in. detail, the forms of the primordial fauna 

 which you have collected, the only head of the Conocephalites^ of 

 which you have sent me the engraving, suffices to show me, that 

 your appreciation of tJie ensemble of that fauna is exact. Besides I 

 am convinced, by all that I know of your works up to this time, that 

 your judgment is correct, and that you are not the man to permit 

 yourself to be led away by preconceived ideas. Therefore the dis- 

 tinction which you have established between the three faunas ; tlie 

 black slates, the white and the grey limestones constitute for me facts 

 which merit all my confidence. 



" I think then as very rational all that you have said on the order 

 of succession. If the locality at Quebec, does not admit of the deter- 

 mination, in an evident manner, of the relative age of the three 

 faunas, by observation of their superposition, that which is the fun- 

 damental proof in palaeontology as it is in stratigraphy, I think you 

 will discover some other locality, in which may be more clearly 

 decided that relative age. 



" In the meantime we can only judge from the nature of the fossils. 

 As to those of the white limestone, such as you have recognized th^m, 

 they indicate clearly a stage of the primordial fauna. Whether that 

 stage is above or below that of the Potsdam, or whether it represents 

 the same horizon as the latter, is a question of secondary and local 

 importance, which probably will be solved in time. There may be 

 several stages distinct from each other in America as in Sweden, 

 while I recognize only one in Bohemia. These are only such diver- 

 sities as we ma)'^ expect in countries distant from each other. 



" The fauna of the black slates, as you have described it in your 

 letter, consisting almost entirely of Graptolites with two Lingulse, a 

 Discina and a small trilobite, does not present a decisive character 

 like that of the white limestone. We cannot then, on the first view, 

 declare that it constitutes a stage of the primordial fauna. But if 

 these black slates are the same as those which have furnished the 

 three species of Olenus in Vermont, there can be no hesitation, and 

 it will be necessary to recognize also that fauna, in that schistose 

 mass. In that case, the occurrence of the graptolites, in such great 

 numbers on that horizon, would be a very remarkable phenomenon, 

 of which we have no example in other Silurian regions. It would be 

 necessary to recognize, in that fact, a new proof, of the remarkable 

 privilege of anteriority, which I have signalized for the zone of the 

 North, of which your country forms a part. As to the small trilobite 

 found in these slates, its dimensions calls forth the thought that you 

 may discover the metamorphoses (of trilobites) in that formation. 



<' The fauna of the grey limestone is well characterized as apper- 

 taining to the second fauna, as you have observed, for it presents the 

 ordinary genera of Trilol)ites, Cephalopods, Gasteropods, &c. The 

 presence of one species oi Ai/nos(iis, is also very natural, since that 

 Genus is found in other Silurian countries, just up to the superior 

 limit of the second fauna, for example, in Bohemia just in d 5. 



