[bailey] volcanic ROCKS OF NEW BRUNSWICK 127 



porphyries and breccias. The largest areas now exposed are a few miles 

 east of St. John, in the neighbourhood of Lodi Lomond and Hammond 

 river, though others, hardly less conspicuous, are to be seen at some other 

 points, notably near the Nerepis Hills. It would seem that during the 

 period in question volcanic overflows, both aereal and marine, character- 

 ized much of southern New Brunswick as they did much of the Atlantic 

 sea-board of America, and that these conditions prevailed for a very 

 considerable period, the thickness of the accumulations having been 

 estimated (in St. John county) as not less than 10,000 feet. 



Some years ago a collection of these supposed Huronian rocks of 

 southern New Brunswick, made by the writer, were placed in the hands 

 of Dr. W. F. Matthew, then of Columbia University, New York, and 

 by him examined petrographically, with the result of finding that the 

 Pre-Cambrian dykes of the disti'ict, whether in association with Lau- 

 rentian or Huronian strata,, were of the nature of diabases, while those 

 of later origin appeared generally to be augite-porphyri te and basalt. 

 The so-called felsites are usually fine grained admixtures of quartz and 

 felspar, generally very flinty and hence in the earlier reports often 

 designated as petrosilex, and not unfrequently porphyxitic witth minute 

 crystals of orthoclase. The breccias or agglomerates are an especially 

 noteworthy feature, indicating the rapid shattering, proba-bly under 

 water, of the lava-rock, and its subsequent recompacting into a mass so 

 solid that only upon weathered surfaces or in microscopic sections can 

 its true nature be recognized. The vesicles in the amygdaloids are 

 sometimes filled with quartz, sometimes with calcite, and epidote and 

 chlorite are of frequent occurrence, but zeolites, such as abound in the 

 more recent eruptive rocks, appear to be wanting. Fluidal structures 

 and 'lines of ûow" may sometimes be observed. 



Cambrian. 



The rocks referred to the Huronian in New Brunswick are fol- 

 lowed up, and unconformably, by the Etcheminian group of Matthew, 

 which, though yielding fossils, is regarded by that writer as also Pre- 

 Cambrian. In it volcanic products continue to be a conspicuous feature, 

 though these no longer predominate as compared with those of clastic 

 origin. They seem to mark a gradual lessening of volcanic activities 

 which in the true Cambrian almost disappear. D3^kes it is true occur, 

 but unless interbedded with the Cambrian strata it is not possible to as- 

 sign these to a definite horizon, and some of them may bo of much later 

 origin. In his studies of these d3'kes, such as penetrate Cambrian slates 

 at Barlow's Bluff, Dr. W. D. ]\Iatthew found them to consist of home- 



