of the Island of Tasmania. 159 



proportions somewhat different, but in which the hornblende 

 predominates. They vary, also, in their structure, being — 

 1. slaty; 2. prismatic; 3. amorphous. 1. Slaty greenstones 

 or schistoid Diabase. Colour, in recent fracture between 

 leek and pistachio green, decomposing on the external 

 surface to a dull reddish brown. Internal surface has a waxy 

 lustre. The imbedded crystals of hornblende are generally 

 brilliant. Its structure is schistose, but the layers are never 

 parallel, and are running from a thickness of two or three 

 inches to a wedge-like termination. For the most part its 

 seams present a lenticular form resembling convex lenses, 

 thus (says the Count) beautifully illustrating the successive 

 overflowings of the incandescent matter. It does not adhere 

 to the toncrue, and exhales an argillaceous odour. The 

 streak varies. Its powder is a brownish yellow colour. 

 Structure, compact and hard. The Count adds that the 

 localities which supply the most important facts bearing on 

 its geological relation are between Launceston and Mount 

 Direction, Mount Direction and George Town, Stony Head, 

 Cape Portland and St. Patrick's Head, Break-o'-Day River 

 and the Tyne, Ben Lomond, Ben Nevis, Port Sorell, 

 Day's Bluff, Lake Arthur, Lake Sorell, the Great Lake, 

 Lake St. Clair, Western Bluff, Mount Cradle, and the source 

 of the Nive, and Mount Cameron West. He says, also, that 

 this variety of greenstone occurs at various heights, capping 

 all the prominent elevations of the interior of the island. 

 It is invariably and intimately associated with porphyries, 

 argillaceous schist, mica, slate, syenite, granite, siliceous 

 slate, and limestone. When it is isolated from the prismatic 

 or amorphous greenstone, its seams are horizontal. When, 

 however, these varieties are in contact with it, the seams 

 are vertical, broken, and distorted. 



The examination of the great area which this schistose 

 greenstone covers in Van Diemen's Land, leads to the 

 discovery of sources from which it overflowed the island. 

 The principal sites appear to have existed in the vicinity 

 of Cape Portland, between Mount Barrow and Mount 

 Arthur, on the north side of Ben Lomond, on Mount St. 

 Patrick, at Port Sorell, on Mount Cradle, Mount Cameron 

 West, and at the source of the Nive. In all these places the 

 schistose greenstone is associated with porphyry. This 

 association strongly led the Count to believe that the 

 greenstone flowed along the pre-existing slope of the conso- 

 lidated porphyry. 



