Me Learn — Silurian Arisaig Series of Arisaig, N. S. 127 



range of the species as given by Schuchert and Twen- 

 hofel were only intended to be preliminary and deal 

 chiefly with well-known American forms. The peculiar 

 faunal content and its relation to the muddy seas of 

 Arisaig has been briefly noted by Schuchert and Twen- 

 hofel (1909, 1913), but the details of response to the silt 

 factor and the evidence for its operation have not been 

 considered. In paleogeography the transatlantic affini- 

 ties of the fauna have been recognized since the time of 

 Honeyman (1859). The overlying Knoydart formation 

 has been referred to the Lower Devonian by Ami (1901). 



Scope of present investigation. — The present investi- 

 gation differs from that of all previous workers by deal- 

 ing primarily with the purely paleontological problems 

 of the Silurian. In spite of all that has been done at 

 Arisaig, the whole fauna is now assembled and syste- 

 matically studied for the first time. That this is neces- 

 sary is shown by the fact that eight new genera, 

 forty-nine new species and twenty-seven new varieties 

 have been erected, and many species not previously recog- 

 nized in this fauna have been identified. With the 

 taxonomic work as a basis, the problem is expanded to 

 include the zonal range of all the species, the evolution 

 of the fauna, the biological associations and their causes, 

 correlation with Great Britain and Maine, and finally the 

 paleogeographic relations. While the age of the over- 

 lying Knoydart formation and its relation to the Arisaig 

 series are not solved, the whole problem is restated and 

 a Silurian age suggested. 



The entire work, including the description and illus- 

 tration of all the species, and the bibliography, is to be 

 published by the Geological Survey of Canada. For this 

 reason, only a summary of the main results, together 

 with a preliminary description of the new genera and a 

 few new species, is given below. The complete taxo- 

 nomic treatment of the fauna, its evolution and zonal 

 arrangement, full faunal lists, etc., are reserved for the 

 final report. 



Acknowledgments. — The whole investigation has been 

 carried out under the constant supervision of Professor 

 Charles Schuchert of Yale University and has thus bene- 

 fited bythe long experience of that research worker in 

 Paleozoic stratigraphy. The author is under obligations 

 to other members of the Department of Geological 



