120 The Sedimentary, Metamorphic, 



crossed by dykes of quartz porphyrite,and still later by dykes 

 of diabase, finally in tertiary times by a few djkes of 

 basalt. 



The confused manner in which the various classes of 

 rocks are "jumbled" together at Ensay, often within the 

 space of a few yards, is due to their being part of an 

 approximately horizontal contact plane, wherein they have 

 been all welded into a complex whole. 



Regional and Contact Metamorphism. 



An important question now awaits some reply, What has 

 caused the peculiar- metamorphism of the Ensay sediments? 

 That is to say — Why is it that, although in contact with 

 intrusive igneous masses, metamorphism has, in this instance, 

 converted the sediments into mica schist and gneiss, and not, 

 as is the case in other intrusive areas in Gippsland, into 

 rocks of the hornfels type ? 



It seems that there may be two alternative replies, one 

 being that the schists were regionally metamorphosed before 

 the plutonic masses invaded them, and the other that they 

 are no more than abnormal instances of contact action. 



The schists at Ensay are most probably the metamorphosed 

 sediments of the district. Their mineral and structural 

 character is that of the regional schists of Omeo, and not 

 that of the contact schists. It seems that they were meta- 

 morphosed before they were invaded by the plutonic rocks, 

 yet, like the contact schists, they are most altered in the 

 neighbourhood of the igneous masses. 



Any explanation which is satisfactory must reconcile these 

 seeming contradictory phenomena. 



I have already drawn attention, at page 110, to the three 

 types of more or less metamorphosed Silurian sediments in 

 North Gippsland, and of which the argillites are the least 

 altered. Their molecular re-arrangement — that is to say, 

 the re-crystallisation of their argillaceous parts — is one of 

 the lesser stages of metamorphism as I observe it in this 

 district. I note, further, that it is clearly connected with 

 the folding together of the strata; for rocks of this class, 

 which have been most disturbed, folded, and crushed 

 together, are also most altered in their mineral structure. 

 This may be observed in wide tracts, where there are no 

 surface indications of the proximity of igneous rock masses 

 to which such alterations might be attributed. 



