48 



abundance, and although highly bitumenized, the concentric 

 layers may frequently be traced. Sections of these, prepared 

 for the microscope, will doubtless shed some additional light 

 upon the subject. 



A bed of lignite crops out in the channel of the Eiver 

 Tamar, and from its position it seems to be one of the lowest 

 members of the Launceston series. 



It lies unconformably upon inclined Greijwaclce, a short 

 distance below Rostella. — {See Fig. 31.) 



A section of the greywacke beds is exposed along the shore 

 of the West Tamar, upon Dr. Maddox's property, where a 

 quarry has been worked for some time, and from which the 

 freestone for the Launceston Mechanics' Institute has been 

 obtained. 



The strike at this point is in an easterly direction across 

 the Tamar. Dip about 30 degrees to the horizon south-east. 

 From a rough computation of the oblique, or exposed, surface 

 I obtained the following measurements, viz, : — 



Thickness. 



1 . Intrusive greenstone — 



2. Close-grained greenish-grey sandstone, worked ) i OO f f 



some time for building purposes ] 



3. Micaceous flagstone 78 ,, 



4. Reddish fissile shales 60 



5. Laminated flags and shales 1 00 , , 



6. Sandstone 60 ,, 



7. Band of black homogenous shale, with peculiar ) 9 " "h 



grooved markings ] " ^^^ ^^' 



8. Sandstones and shales, obscured by stone \ 



boulders and gravel 3 



Total thickness exposed, say 400 Feet. 



(^ee Fig. 31.) 



The bed of lignite which rests upon, or is flanked by these 

 beds, is very probably a continuation of the Breadalbane 

 deposit, and should it prove to be so — it, together with the 

 distribution of the opalised woods — will be of good service in 

 determining the relative positions of the several beds within 

 this hitherto neglected series. 



It would be premature on my part to attempt to define the 

 relative position of these beds as the data at the command of 

 one individual is too meagre to form a conclusion with any 

 degree of confidence. Notwithstanding this, there are suffi- 

 cient grounds for the determination of three zones within the 

 Tamar valley. These I may call the Upper, Middle, and 

 Lower Zones. I do not mean that these zones are to be 

 considered as distinct, because of a marked difference in the 



