2l6 



of a portion of the Riversdale-Union area in a region from 

 which considerable palaeontological evidence is forthcom- 

 ing to indicate that the strata are not of Devonian age but 

 are approximately the equivalents of the Millstone Grit 

 and therefore of Upper Carboniferous or Pennsylvanian 

 age. 



For various reasons Fletcher in working out structural 

 details made little or no use of fossils but instead depended 

 solely on stratigraphical methods, and in making corre- 

 lations was guided almost entirely by structural and litho- 

 logical characters. Furthermore, during the course of his 

 long life work, as he extended his mapping from the 

 extremity of Cape Breton on the east to and over the Car- 

 boniferous areas of the mainland, his views regarding the 

 classification of the Carboniferous changed, but yet, in 

 deference to established custom or for other reasons, the 

 classification as expressed on his maps remained essentially 

 unchanged. As an instance in point, it may be noted that 

 under the term Carboniferous Conglomerate was classed on 

 earlier maps a thick series of coarse sediments supposed to 

 mark the base of the Carboniferous system; on later maps, 

 the term was made to include also a series of shales, etc., 

 recognized as representing the Horton series; while on 

 still later maps, the older meaning of the term Carboni- 

 ferous Conglomerate was readopted and the Horton beds 

 were mapped as Devonian. Besides the difficulty of 

 interpreting Fletcher's maps arising from the conditions 

 outlined above, a student is confronted with another 

 difficulty due to the fact that if not personally acquainted 

 with the field he is not in a position to understand why, for 

 instance, the area of rocks indicated on the accompanying 

 map as lying north of Riversdale and wholly enclosed by 

 'Devonian', was classed as Carboniferous Conglomerate, 

 i.e. as the basal portion of the Carboniferous, and not as 

 some higher member of the system. The explanation 

 seems to be that Fletcher from his studies of such sections of 

 the Carboniferous as are exposed at Sydney and Joggins, be- 

 came convinced that the Carboniferous system where most 

 fully developed, consists in ascending order of Conglomerate 

 series. Limestone series, Millstone Grit, and Productive 

 Coal Measures, and furthermore that the Conglomerate 

 series was more or less local in its development and that in 

 many places the Limestone series forms the base of the 

 Carboniferous. 



