VOLCANIC ROCKS OF THE MARITIME PROVINCES. 79 



Over tlie Laiirentian are great thicknesses of beds com- 

 posed of surface volcanic rocks, which have been divided 

 into three or four groups in the southern part of the pro- 

 vince, but which are conveniently classed together as 

 ITuronian, if the term be used in its broader sense, or, if 

 this be disallowed, must be simply called pre-Cambrian. 

 These form the greater part of the southern metamorphic 

 hills, and occur in small patches north of these. The 

 high broken country about the headwaters of the Tobique, 

 Nepisiguit and North-west Miramichi, is composed of 

 pre-Cambrian rocks, largely eruptive, and intrusive 

 granite. 



These volcanic rocks are known for the most part 

 only through field descriptions. They are hard, fine- 

 grained liinty rocks, mostly red or dark colored ; some 

 time, though not generally, schistose ; and not always 

 recognizable as of igneous origin. Those from a part of 

 the southern metamorphic hills have been studied by the 

 aid of the microscope and are then seen to show all the 

 characteristic structures of volcanic products in great per- 

 fection. They evidently were once i)recisely like the 

 lavas and ash-rocks of modern times. The changes they 

 have undergone are mostly limited to the devitrification 

 of the glassy parts and the partial or complete recrystal- 

 lization of some of the minerals. 



The deep-seated crystalline facies of these effusives is 

 not well known. They maj' perhaps be the surface equi- 

 valents of some of the granites and other intrusives in 

 the Laurentian rocks ; but this remains to be proved. 

 Although many instances are recorded by the New Bruns- 

 Avick and Nova Scotia geologists of transitions from granite 

 into felsite, yet none can be taken as satisfactoiy without 

 the support of thin sections and chemical analyses to prove 

 their identity in composition, and a careful study of the 

 progressive gradations from one to the other. 



