46 



shoe shaped indentation, within which the town of Launceston 

 is situated, and for the ever-shifting series of beds which 

 compose the Windmill Hill. 



An important feature in the Launceston beds is the altera- 

 tion that appears to have taken place in the tufaceous sands. 

 Here and there, in irregularly disposed horizontal bands, occur 

 indurated ferruginous nodules of tufaceous sand or clay. 

 These nodules have frequently for their centre a core of blue 

 clay, which has in most cases filled up the cavity of a hollow 

 tree or branch. 



On splitting open one of these nodules it invariably pre- 

 sents the appearance of a section of an exogenous tree, with 

 regularly disposed concentric rings round an indurated vitre- 

 ous or ferruginous pith. 



On closer examination, however, we observed that although 

 the iron-coloured rings present the appearance of a nodule 

 formed by a succession of layers, like the coats of an onion, 

 yet the laminations are disposed horizontally, as in the sur- 

 rounding strata. This is more fully substantiated by the 

 casts of leaves being disclosed in laminae at right angles to 

 the ferruginous rings, which envelop the nodule where these 

 latter rings are at right angles to the surrounding beds. — (See 

 Fig. 25a.) 



It is thus proved that, subsequent to deposition as a soft, 

 porous mass, the ferruginous particles have, by a process of 

 segregation, gathered together in rings round an attracting 

 centre ; these rings approaching closer and closer to the 

 centre as the process continued, until in many cases the 

 nodule is converted into brown hematite. 



It would appear, therefore, that the beds of the Middle 

 Zone are in most cases principally formed of the scoriae and 

 ashes of active volcanoes in the immediate vicinity of Laun- 

 ceston ; that the waters, although locally and periodically 

 affected chemically by the substances with which it comes 

 in contact, was on the whole, capable of sustaining animal and 

 vegetable life, while its borders supported a most luxurious 

 vegetation of types as shown. (Figs. 1 to 10.) 



Generally, then, we may characterize the Middle Zone as a 

 series of beds, deposited during the period of volcanic activity. 



THE UPPER ZONE. 



The Upper Zone is well represented by those low rounded 

 hills and terraces flanking the present course of the Eiver 

 Tamar. They are principally composed of alternate beds of 

 conglomerates, breccias, and gravels, and the detritus of the 

 lower zones. (Fit/. 30.) 



Prominent among them all, we recognise the partially 



