424 CAMBRIAN AND SILURIAN IN NORTH AMERICA. [XV. 



ing the group both with the true Silurian, to which it has 

 very generally been united, and with the Cambrian, of which, 

 from the first, it has formed a part. I therefore venture to 

 suggest the name of Siluro-Cambrian, as a convenient syno- 

 nyme for the Upper Cambrian of Sedgwick (the Lower Silu- 

 rian of Murchison), corresponding to the second fauna ; reserv- 

 ing, at the same time, the name of Cambrian for the rocks of 

 the first fauna, the Lower and Middle Cambrian of Sedg- 

 wick, and restricting, with him, the name of Silurian to the 

 rocks of the third fauna, the Upper Silurian of Murchison.* 

 The late Professor Jukes, it may be here mentioned, in his 

 Manual of Geology, published in 1857, still retained for the 

 Bala group the name of Cainbro- Silurian (which had been 

 withdrawn by Sedgwick in 1854), and reserved the name of 

 the " true Silurian period " for the Upper Silurian of Murchi- 

 son. In his recent and much-improved edition of this excel- 

 lent Manual (1872), Professor Giekie, the director of the 

 geological survey of Scotland, has substituted the nomencla- 

 ture of Murchison ; with the important exception, however, 

 that he follows Hicks and Salter in separating the Menevian 

 from the Lingula flags, and uniting it with the underlying 

 Harlech rocks (as has been done in the table on page 386), 

 giving to the two the name of Cambrian (loc. cit., pages 526 - 

 529), and thus, on good paleontological grounds, extending 

 this name above the horizon admitted by Murchison. Bar- 

 rande, on the contrary, in his recent essay on trilobites (1871, 

 page 250), makes the Silurian to include not only the Lingula 

 flags proper (Maentwrog, Festiniog, and Dolgelly), but the 

 Menevian, and even a great part of the Harlech rocks them- 



* Dr. Dawson, in his address as president of the Natural History Society 

 of Montreal, in May, 1872, has taken the occasion of the publication in the 

 Canadian Naturalist of the first and second parts of this history, to review 

 the subject here discussed. Recognizing the necessity of a reform in the 

 nomenclature of the palaeozoic rocks in conformity with the views of Sedg- 

 wick, he would restrict to the rocks of the third fauna the name of Silurian, 

 making it a division equivalent to Devonian ; and while reserving, with Lyell, 

 Phillips, and others, the name of Cambrian for the first fauna only, agrees 

 with me in the propriety of adopting the name of Siluro-Cambrian for the 

 second fauna. 



