CHAP. XXV 
CLOSE OF THE PLATEAU-ERUPTIONS 
413 
deposition of the Hui’let Limestone. As the area sank, 
of the Calciferous Sandstones crept over the lianks of 
the trachytes, until at last they had completely buried 
these rocks before the limestone spread over the area 
(Kg. 141). In consequence, probably, of the uneven 
surface of this plateau, there is here a strong overlap 
of the higher part of the Calciferous Sandstones. On 
the west side of the volcanic area there can hardly 
be more than some 200 feet of strata between the 
top of the trachytic series and the limestone, while 
on the south side there must be greatly more than 
that thickness. This structure probably indicates that 
the Garleton volcanoes became extinct after having 
piled up a mass of tuffs and lavas to such a height 
that its summits were not submerged until the area 
had subsided 800 or 1000 feet in the waters, over the 
floor of w’hich the Calciferous Sandstones were laid 
down. Hence, in spite of the proximity ol the lavas 
to the limestone, there may have been a vast interval 
of time between their respective epochs, as has been 
already suggested with regard to other plateaux. 
This subject will be again referred to in discussing 
the relative chronology of the plateaux and puys. 
In the Berwickshire and Solway districts, the 
extinction of the plateau-vents appears to have taken 
place at a still earlier part of the Carboniferous period, 
for there the andesites, while they rest on the Upper 
Old Eed Sandstone, are covered with at least the 
higher group of the Calciferous Sandstones (Fig. 142). 
The equivalent of the Hurlet Limestone of Central 
Scotland must lie many hundred feet above them. 
The submergence of the plateaux, and their en- 
tombment under the tliick Carboniferous Limestone 
series, did not mark the close of volcanic activity 
in Central Scotland during Carboniferous time. The 
plateau-type of eruption ceased and was not repeated, 
but a new type arose, to which I would now call the 
reader’s attention. 
the successive 
zones 
Pro. 142 .— Section acros.s the Solway plateau from Birrcirswavk to Kirtlehridge. 
. Upper Silurian strata ; 2. Upper Old Red Sandstone ; 3. Plateau-lavas ; 4. Calciferous Sandstones and Carboniferous Limestone series ; 6. Trias. 
