508 | Notices of Memoirs—W. H. Hudleston— 
presence of pseudomorphs of chloride of sodium, show that a new 
condition of things set in with the Keuper. In conclusion, I may 
point out while on negative evidence that the absence of saline 
deposits in the Bunter is on the other hand against the subaerial 
river-delta hypothesis, as the sandy deposits to which they are com- 
pared often eventually absorb the rivers which create them ; and this 
applies to the North of Africa as well as to the Asiatic example. 
INKS Zens (Oeey AM rasan Oatisysie 
Tue Grotocy or Devon, Facts anD INFERENCES, FROM THE 
PRESIDENTIAL ADDRESS TO THE DervonsHirnE AssocratTion. By 
W. H. Hupuzsron, Esq., F.R.S., Sec.G.8., ete. August, 1889. 
Part II. 
(Concluded from November Number, p. 514.) 
Tavistock CounTRY. 
\HE geological phenomena in the neighbourhood of Tavistock are 
of such interest that I cannot do better than close this address 
with a brief allusion to some of the features of the west side of 
Dartmoor, and the adjacent country. 
It is a region which has always presented peculiar difficulties, but - 
the new line of railway in course of construction may help to clear 
matters up. The subject can be grouped under four headings: 
{1) The structure of the country; (2) the nature of the basic 
igneous rocks, or ‘‘greenstones”; (3) Dartmoor; (4) the metal- 
liferous deposits. 
(1) The structure of the country on the west side of Dartmoor 
differs considerably from that on the east side, more especially in 
the fact that the Devonian beds are represented as dipping towards 
the sea instead of away from it; at least this is the case for several 
miles immediately north of Plymouth. Further towards the north, 
in the direction of Tavistock and beyond, there would seem to be 
a complexity of structure unusual even for Devonshire. Con- 
sequently the boundary between the Devonian and Carboniferous, 
as laid down in the Survey Map, may be subject to considerable 
revision. Mr. Worth astonished us lately at the Geological Society 
by the statement that the town of Tavistock is actually on the 
Carboniferous, and yet that, owing to a complex series of foldings, 
the Devonian rocks are brought up on both sides.. I know of no 
spot in the United Kingdom where the geological boundary-lines 
seem to be so much under discussion at the present moment. 
Although Mr. H. B. Woodward, in the map attached to the 
“Geology of England and Wales,” follows De la Beche in assigning 
the Brent Tor district to the Carboniferous, it has long been claimed 
as Devonian by some geologists. These views are perhaps the 
result of Mr. Rutley’s interesting work on the schistose volcanic rocks 
west of Dartmoor, described as consisting of alternations of lava- 
flows, tufis, and tufaceous sediments. That this class of rock, locally 
