160 
of No 8, and forming the southern margin of the culm-trough, 
Mr. Williams has been led to conclude, that the floriferous beds, by 
other arcs of undulation, have broken through the thinner northern 
border of the killas, throwing it off on each shoulder and intercepting 
it in troughs. Instances of this, he says, are sufficiently appa- 
rent on each side of a line drawn from Greston Bridge on the 
Tamar, S.E. of Launceston, to Heath Field, north of Tavistock; the 
high central ridge consisting of floriferous and Coddon girts, flanked 
on the north by undoubted killas and volcanic ash and breccia. ‘To 
the N.W., W.S.W. and 8S. of Greston Bridge, the floriferous 
series is stated to be exposed in great force, extending almost un- 
interruptedly in a straight line into the great body of the culm-field ; 
but to the west it is said to be generally concealed by killas, though 
a continuous contracted range branches off to the westward by 
Lezant, Lawanick-down, and Alternau; and it appears to be depressed 
under, or to pass into the killas and speckled slates of Davidstow, 
N.E. of Camelford. 
A small area of an inverted arc of undulation is exposed in and 
around Tavistock ; and the floriferous grit, principally identified by 
its associated slates, is stated to underlie the high killas range of 
Whitcombe Down on the south; and on the north to be laid open in 
the road to Launceston, similarly associated, with the additional ac- 
companiment of intercalated killas and Coddon Hill grit dipping 
beneath the volcanic ash of Marly Mead. Mr. Williams also mentions 
a shaft sunk in a copper lode close by the turnpike gate on the road 
from Tavistock to Callington, as another instance of floriferous grit, 
or a rock exactly the same as that which contains the copper lode of 
Wheal Friendship, underlying pale green slate or killas: and he 
adds, there can be no doubt that Wheal Friendship mine is in No. 9 
or the floriferous series. The next instance mentioned in the paper, is 
at Linkinghorn and South Hill, north of Callington, where there is 
stated to be an entire suite of alternations of killas, Coddon grits, and 
floriferous grits with plants, all dipping south. Again, near Pillaton, 
between Callington and Saltash, there are said to be countless minor 
alternations of floriferous and Coddon grits, each thinning out and 
interlocking like the teeth of a trap. Another instance of the killas 
overlying the floriferous grit, is said to occur in a hill at Penter’s 
Cross on the road from Callington to Saltash, where a cutting ex- 
hibits in the lower part, a series of alternations of floriferous sand- 
stone, and culmy slates which in ascending disappear, and in their 
place a delicate pale green killas alternates with the sandstone 
beds, while at the summit the sandstones disappear and are replaced 
altogether by killas. A fault traverses the hill, and to the south of 
it only killas occurs. 
The general results of his observations, Mr. Williams says, 
show, that in the ascending order, from Cannington Park and the 
Quantocks in Somersetshire, to the Land’s End, there is a group 
constituted of ten strikingly simple, consecutive series, severally 
varying in their mineral and zoological character; that as respects 
the limestone suites, the thin and spare dimensions of such as occur 
