560 Notices of Memoirs—W. H. Hudleston— 
linear, and is probably not absolutely confined to any particular 
geological horizon. 
The interbedded basic igneous rocks have been described by 
numerous authors, and their general petrographic features are fairly 
well known. In Northern Cornwall, according to Mr. J. A. Phillips, 
these ancient lavas are called ‘“dunstones.” Specimens analyzed 
by him were found to contain 42 per cent. of silica, over 20 per 
cent. of alumina, and the alkali is almost entirely soda: the amount 
of lime is nearly twice that of magnesia, and there is over 12 per 
cent. of protoxide of iron. From a chemical point of view these 
rocks, then, are allied to the basalts. 
The intrusive ‘“ greenstones” are classed by Mr. Worth under 
three heads. They are sporadically developed, but seem to be most 
numerous and of the largest size in the vicinity of Dartmoor: they 
are believed to be older than the Dartmoor granite, which is said to 
alter them. If the Survey mapping is correct, the so-called gabbros 
between Marytavy and Wapsworthy occur in Carboniferous rocks, 
and must of course be younger than the beds into which they are 
intruded. ‘These gabbros, Mr. Worth considers, are the vestiges of 
a widespread pre-Dartmoor igneous activity, producing basic rocks. 
He points out that their relations to the granite, both here and in 
Cornwall, are too persistent to be accidental, and he suggests that 
they may represent the basic forerunners of the more acidic granites. 
The age of the rocks into which the Marytavy “gabbros” have 
been injected still remains to be settled, but the notion that either 
they or the granites have brought up the lowest stratified rocks is 
not borne out by experience in other parts of the area round 
Dartmoor. 
(3) Having now cleared the way a little by a brief glance at the 
containing rocks, we are in a position to attempt the study of Dart- 
moor itself, that supreme monument of the old eruptive forces. 
Dartmoor, as every one knows, is contained partly in Devonian and 
partly in Carboniferous rocks, and from the position of the Posido- 
nomya-beds it is probable that the lower part of the Carboniferous 
adjoins the granite. Mr. Ussher, speaking of the beds on the 
northern and eastern flanks of Dartmoor, observes that the Culm- 
rocks dip off the granite above Belstone in a marked manner. He 
also says that the Culm-rocks on the north are roughly parallel in 
their strike to the margin of the granite, whilst on the east and west 
their strike is cut off, so to speak, by the granite or else deflected. 
These considerations are of importance as showing how the granite 
lies in its case. 
From what has already been said, it is perfectly clear that this 
granite is in nowise connected with anything of the nature of an 
anticlinal axis bringing up older rocks. In fact on the east side, 
where it abruptly terminates, its relations to the adjacent country 
are almost those of a synclinal. On the Tavistock side its relations 
with the adjacent country are more obscure, owing to the stratigraphy 
of the district being as yet undetermined. Moreover, there is pro- 
bably underground connection on this side, through Hingston Down, 
with the granite boss of Brown Willy. 
