﻿500 



Canadian Record of Science. 



from the Georgia sandrock of the vicinity and have 

 a considerably higher position in .the geological scale. 



The term Potsdam formation in the discussion of these 

 rocks must be carefully distinguislied from the Potsdam 

 sandstone since the indiscriminate use of the terms 

 has led to a certain amount of confusion in the inter- 

 pretation of these geological problems. 



In the earlier reports of the Geological Survey the 

 term Potsdam was held to include all between the 

 Calciferous and the Huronian as then understood, the 

 sandstone forming the upper member. Since that time, 

 however, the intervening or Cambrian system has been 

 studied, and the formations which compose it have been 

 clearly recognized between the sandstone and the 

 Huronian, and these have yielded a great variety of 

 fossils of Primordial types. These include the rocks 

 of the Georgia formation, which extends into Quebec near 

 St. Armand station from the state of Vermont, but these 

 rocks of the Georgia division are distinct from the 

 Potsdam sandstone formation which has been clearly 

 shown to be simply an extension downward of the 

 Calciferous, and has, therefore, now been included in the 

 Cambro-Silurian system as its lowest member. The 

 Cambrian rocks are developed along the flanks of the 

 Sutton anticlinal, and these underlie the Sillery proper or 

 upper portion of that division, which on the under- 

 standing that the Levis formation is the equivalent of the 

 Calciferous naturally falls into the place of the Potsdam 

 sandstone as a peculiar local development. 



There is yet another portion of the old Quebec Group 

 whicli calls for a word of explanation, viz., the series 

 of diorites, diabases and serpentines, which occur along 

 the east side of the Sutton mountain range ; and which, 

 under the old hypothesis, were regarded as, in large part, 

 the altered equivalents of the sandy portions of the 

 Sillery formation. A careful ^tudy of these masses over 



