this district. The writer would also acknowledge valuable personal 

 assistance from Mr. Fletcher, rendered at the instance of the Director 

 of the Survey. 



In addition to the geological map of Cape Breton, on which the References to 

 Cambrian areas are depicted, references to the Cambrian rocks of the roc ks. 

 island by Mr. Fletcher will be found in the Reports of Progress of the 

 Geological Survey, year 1875-6, pages 389 to 393 ; year 1876-7, pages 

 428 to 437 ; and year 1877-8, pages 1 IP to 16F. In these reports the 

 rocks are described under the head of Lower Silurian, as at that time 

 the Cambrian was not fully recognized in America as a system with 

 distinctive faunas separate from the Lower Silurian. 



Mr. Fletcher explored two narrow valleys of Cambrian rocks on St. 

 Andrews channel, connected with the Boisdale hills, and two others 

 on East bay, in the Coxheath hills. In all these he found the strata 

 highly inclined, and in many of his notes only the strike is recorded. 

 In the larger Cambrian district on the Mira river also, the strata dip 

 at a high angle, so that the structure cannot be inferred from the de- 

 tails given. Thus the structure and succession of the beds could not 

 be determined without some further study in the field. I therefore 

 gave some attention to the distribution of the strata before collecting 

 materials for the study of the fossils. This preliminary work was of 

 importance as it enabled me to place one of the faunas at a horizon 

 lower than the biological indications had warranted. 



CAMBRIAN STANDARDS. 



The standards used for comparison of the faunas are those of Great Cambrian 

 Britain and Sweden. In the lower members of the Cambrian deposits Sweden. 

 of Sweden the faunas are poor and wanting in variety, but the Middle 

 and Upper Cambrian have a full and rich succession of faunas. The 

 richness of the Cambrian faunas of Sweden in trilobites allows of very 

 exact and minute distinctions between the several layers, so that the 

 succession groups have been distinguished by the several faunas which 

 they contain ; and we also have an upward succession of groups each 

 distinguished by a leading genus of trilobites, or other organism, as : 



Olenellus fHolrnia) fauna. 

 Lower Paradoxides beds. 

 Upper Paradoxides beds. 

 Olenus beds or fauna. 

 Peltura beds or fauna. 

 Dictyonema fauna. 



