26 R. W. ELLS ON THE POTSDAM AND CALCIFEROUS 



distinct horizon. The Cambrian of these provinces presumably represents the michlle and 

 lower divisions of the Cambrian system as it is now iinderstood in eastern America. 



In the province of Quebec also, east of the St. Lawrence river, the typical Potsdam 

 sandstone has not yet been recognized north of the area in Huntingdon county, already 

 described. In 1868, Richardson in his investigations on the Sillery and Levis formations of 

 the Quebec group south and east of Point Levis, regarded portions of the sandstone forma- 

 tions of the Sillery division as probably of that age, principally upon the evidence of the 

 presence of a Salterella in certain of the beds. The rocks of the Sillery were by him 

 arranged under three divisions, called upper, lower and middle Potsdam, and supposed to 

 be older than the Levis, which was regarded as of Calclferous age. Of these, a portion of the 

 quartzites was held to constitute the upper member of the Potsdam, while certain slates of 

 various colours with quartzite and limestone conglomerate were assigned to a lower part of 

 the same formation. The rocks of these divisions, however, differ very greatly in character 

 from those of the typical areas already described, and will be referred to again. 



The arrangement of the formations in the geological scale should depend, it is presumed, 

 upon their stratigraphical sequence, where that can be readily made out, and where it is 

 unaffected by serious faults which could disarrange the regular order of succession. This 

 arrangement should of course be supported by the evidence furnished by the fossils contained 

 in the several groups of strata. Sudden changes in the character of the fossils, as from a 

 Silurian to Cambrian fauna, especially when the presence of faults can be clearly recognized, 

 should furnish data for division of formations into great groups or systems. 



The nomenclature of the science has undergone such very great developments within 

 recent years as a consequence of the detailed study of the rocks over wide areas, that the 

 theories and the classifications of early days have of necessity undergone very considerable 

 modifications. The investigations upon the Cambrian rocks in particular, both as regards 

 their stratigraphy, physical characters and fauna have conclusively shown that the strata 

 composing this great system are clearly divisible into several groups, and that the general 

 term Potsdam as applied to the whole Cambrian series can no longer be so employed. 



From the descriptions of the Potsdam and Calciferous formations already given for the 

 typical areas in New York and Canada, it will be readily seen that these two pass into one 

 another without any apparent break and upon stratigraphical grounds, as well as from the 

 fossil evidence, may practically be regarded as one and the same formation. Thus Emmons 

 remarks in his report ' on the geology of the state of New York, 1840, that not only did he 

 regard the two divisions as parts of one formation, but that they may have been contempor- 

 aneous, and that the deposition of the Calciferous sandrock may have gone on simultaneously 

 with that of the Potsdam sandstone, the coarser sandy materials being deposited first, while 

 the tine siliceous matter would be carried further, but would be deposited early and would 

 constitute a regular sandstone ; another portion would be carried still further, and would 

 probably be associated with calcareous particles. These would subside also and would con- 

 stitute a calcareo-siliceous rock. 



The two formations he says, " will difier in two respects, the sandstone will be deposited 

 near the shore and of course in shallow water, which will be indicated by ripple marks, and 

 it will bear or contain only those organic relics which are peculiar to such locations. On the 



' Geology, N. Y., 1840, pp. 347, 348. 



