us 



W. H. Twenhofel — Silurian Section at Arisaig. 



have been true at another period of the shore's history, as 

 the first raised cliff has here a point which is a replica of the 

 lowest one. 



Description of the Silurian Section. 



In order to facilitate the study of the appearance and dura- 

 tion of the species in their true time relations the section is 



Honeyman 

 1864 



Division D. 



Red Stratum. 



Division C. 



Division B'. 

 Total thick- 

 ness B', C, D 

 500 feet. 



Division B. 

 170 feet. 



Division A. 

 200 feet. 



Dawson 

 1868, 1891 



Upper Arisaig. 

 (Lower Hel- 



derberg or 



Ludlow) 



Lower Arisaig 

 (Clinton or 

 Upper Llan- 

 dovery) 



Fletcher 

 1886 



Lower Helder- 

 berg or E 6 . 

 1038 feet. 



Ami 

 1901 



Stonehouse 

 Formation. 



jMoydart 

 Formation. 



Twenhofel 1909 



Red Stratum. 



Niagara or E 2 

 1293 feet. 



J Upper Clinton 



I or E 2 . 



i 148+ feet. 



Lower Clinton 

 or E 2 . 

 345+ feet, 



[Medina or Ej. 



182 feet. 



Division IVb 



or 

 Stonehouse 

 Formation. 



(Ludlow) 



{ Red shales and 

 limestones. 

 9? feet. 



Argillaceous 

 limestones 

 and shales. 

 978 feet. 



Division IVa or 

 Moydart For- 

 mation. 



(Approximates 

 Louisville or 



Wenlock time) 



McAdam 

 Formation. 



Division III or 

 McAdam 

 Formation. 



(Rochester or 

 Upper Llan- 

 dovery) 



i Fault. 



r Red Stratum. 

 32 feet. 



j Argillaceous 

 limestones 

 and shales. 



I 347 feet. 



7 ~~ 



Dark shales. 



Dark shales 

 and 



argillaceous 



limestones. 



1020 feet. 



Arisaig 

 Formation. 



I 



Division II or 

 Arisaig For- 

 mation. 



(Clinton or 

 Lower Llan- 

 dovery) 



f Green shales 

 with thin 

 sandstones. 



) Dark shales 

 with thin 

 sandstones. 



t 833+ feet. 



Division I. 

 (Clinton) 



f Sandstones, 

 limestones, 



and shales. 



t ? 160 feet. 



given beginning at the base and extending upward. Forty 

 zones have been established, the character of the sediments 

 being the basis for division. These forty zones have been 

 grouped in five subdivisions. The thickness for each zone has 



