Section IV., 1884. [ 91 ] Trans. Roy. Soc. Canada, 



& 



IV.— Om Geological Contacts and Ancient Erosio)i in SoiUliern and Central New 

 Brunswick. — Bij L. W. Bailey. 



(Read May 23, 1884.) 



The importance of geological contacts in the determination of the structure and 

 geological history of différent regions is well understood, and in the stndy of the latter 

 these receive, as they deserve, especial attention. While the various formations, in their 

 petrological characters, their thicknesses, and their contained fossils, aiford the data for 

 estimating the conditions of their origin and their relative duration, it is along their lines 

 of junction that we are to look, more than elsewhere, for information as to the circum- 

 stances under which they came to a close ; in other words, for the time and nature of the 

 physical breaks by which the historical record is divided into its separate chapters, and 

 made comparable with those of other regions. 



In the study of the geological structure of the Province of New Brunswick, which, as 

 regards its general features, is now well advanced, a variety of such contacts has been 

 observed and detailed in the geological reports. From the pecxiliar position, however, 

 which this Province occupies with reference to the great north-eastern or Acadian basin, 

 and from the fact of its possessing a larger number of determinable horizons than any 

 other portion of that basin, of which it therefore becomes to a certain extent the key, the 

 consideration of these contacts has an interest beyond the immediate region in which they 

 are found, and suggests conclusions of much wider application. It is the intention of the 

 writer, in the following remarks, to consider briefly some of the more important of these 

 junctions, and the deductions which they may seem to justify. As the passage from one 

 formation to another is usually accompanied by evidences of more or less extensive 

 erosion, and as this, in some instances, affords almost the only proof of a want of continuity, 

 some observations on this latter point may also prove of interest. 



The reference of a portion of the rocks of soïithern New Brunswick to a pre-Silurian, 

 Azoic, or, as it is now better termed, Archeau age, was first asserted by the writer in con- 

 nection with Mr. Gc. F. Matthew in 1865, on the ground of their relations to the fossil- 

 iferous rocks of St. John, then first identified by Hartt as containing a tyx^ically Primor- 

 dial fauna. It is remarkable that, while the recognition of this ancient horizon is 

 not exceeded, as regards the completeness of the data, by that of any subsequent formation, 

 so its relations to the underlying rocks are of the most satisfactory and conclusive charac- 

 ter. For not only do they differ wholly in lithological characters, a feature which some 

 writers suppose to have been the only ground for their separation, but, in every particular 

 ordinarily marking discordance of successive formations, the evidences here offered are 

 wide-spread and complete. Whatever view be taken as to the precise equivalence of the 

 underlying groups which have been compared respectively with the Laurentian and 

 Huronian systems, the fact remains that these represent a vast thickness of sedimentary 



