Tertiary Voleame Plateau. 391 
(8, p. 241), though it is unlikely that this condition obtained over 
the ‘land-bridge’ in its entirety at any one time; it is more 
reasonable to conceive of temporary oases, limited in extent, 
themselves migratory. 
Toe TIME REPRESENTED BY THE Rep Parrrnes. 
If the red partings are regarded as weathered lavas it must be 
recognized that they represent the lapse of a considerable interval of 
time, for even if they originated under climatic conditions similar to 
those which obtain in India to-day the growth of the Indian laterite 
is exceedingly slow. But if these partings are weathered tufts, 
which from examination in the field and laboratory, ,and also by 
analogy from the deposits of the modern desert of the Oda%ahraun, 
would seem to be the rule, the length of the inter-eruptive period is 
considerably diminished for two reasons. One is that, as has been 
pointed out above, volcanic. ash is far more readily attacked by the 
palagonitic decomposition process than lava, and the other is that 
the red parting covering a lava may represent material which had been 
thrown out and blown over the plains long before the outflow of the 
lava with which it is ultimately associated. Thus we could conceive 
of two flows extruded in one week being separated by a parting. 
This is an extreme case, but we have definite evidence that the 
duration of the period represented by the red partings was 
relatively short. 
At the entrance to the Seydisfjord (Hast Iceland), between 
Dalatangi and Shalanes, acid and basic rocks are exposed in 
a magnificent cliff section which has been figured by Helland 
(4, fig. 10). The main mass of the acid rock is a plano-convex 
shaped lens of liparite with a maximum thickness estimated at 
300 feet, resting on, surrounded, and overlain by an almost horizontal 
series of basalts and red partings. Underlying the whole of this is 
_ a thickness of acid tuff and breccia. The cliff-face is almost vertical, 
and it was impossible to examine much of the section with the 
hammer. At one place it was found that the thinner lower exposure 
of acid rock is a green tuff-breccia, rudely stratified, and containing 
blocks of basalt and banded liparite up to 2 feet in length. ‘I'he 
thick main mass of liparite is a fine-grained greyish rock with 
prominent flow-banding. At its lower boundary it passes into a black 
obsidian about 14 feet thick with a breccia-like under-surface. 
As far as could be seen this obsidian band composes the periphery of 
the liparite throughout the section, with the exception of the eastern 
portion, which has been denuded away. The most interesting part of 
the mass is its western termination, and as it was not possible 
to land at that point I had to be content with making a sketch which 
is reproduced in Fig. 3. The relations of the basalts and red partings 
to the obsidian margin of the liparite are clearly shown. The former 
retain the approximate horizontality which characterizes the whole 
of the bedded basalts of the cliff section. 
The liparite is extrusive, as shown by— 
1. The undisturbed basalts. 
2. The nature of the junction of the obsidian and basalts iilusteated 
