20 
THE CARBONIFEROUS VOLCANOES 
BOOK VI 
In some eases there is evidence of more than one outflow of lava in the 
same band of toadstone. Jukes believed that each band “ was the result, not 
of one simultaneous ejection of igneous matter, but of several, proceeding 
from different foci uniting together to form one band,” and he found that 
near Buxton, two solid beds of toadstone could be seen to have proceeded 
from opposite quarters towards each other without overlapping. 1 
In Millersdale the authors of the Geological Survey Memoir on North 
Derbyshire observed that a band of toadstone about 100 feet thick showed 
six distinct divisions, which they were disposed to regard as marking so 
many separate beds. 2 In Tideswell Dale, on the west side of the valley, 
immediately to the south of the old toadstone quarry, two bands of toadstone 
are seen to be separated by a few yards of limestone. 
(b) Lavas with Tuffs. — It will probably be found that in many, if not in 
most cases, the outflow of lava was preceded, accompanied or followed by 
fragmental discharges. As far back as 1 8 6 1 , J ukes noticed that a toadstone 
band, about 50 feet thick, near Buxton consisted of two solid beds of lava 
“ with beds of purple and green ash, greatly decomposed into clay, both above 
and below each bed and between the two.” 3 
An interesting section, showing this intercalation of the two kinds of 
material is exposed at the lime-kilns beyond the southern end of the railway 
viaduct at Millersdale Station. Over a mass of solid 
blue limestone (1 in Fig. 183) lies a band of bright 
yellow and brown clay (2), varying from six inches to 
two feet in thickness. This may be compared with 
the clay found above the limestone at Peak Forest 
(Fig. 181). But it is probably a layer of highly 
decomposed tuff. It is succeeded by a thin band of 
greenish limestone (3) containing an admixture of fine 
volcanic detritus, and partially cut out by an irregular 
bed, four to eight feet thick, of a highly slaggy, greenish, 
decomposing, spheroidal and amygdaloidal diabase (4). 
This unmistakable lava-sheet is followed by a bed of 
green granular tuff (5), which in some places reaches 
a thickness of three feet, but rapidly dies out. Over a 
1,1 kiln,° ^south^of n Viaduct j S P ace several >’ ards in breadth, the succeeding strata 
Millersdale station. are concealed, and the next visible rock is a dark, 
compact dolerite which weathers spheroidally (6). 
(c) Tuffs without Lavas. — Mr. Bemrose has shown that some of the 
bands of toadstone consist entirely of bedded tuff. In these cases, so far 
as the present visible outcrops allow us to judge, no outflow of lava accom- 
panied the eruption of fragmentary materials. But that the ejection of these 
materials was not the result of a sudden spasmodic explosion, but of a 
continued series of discharges varying in duration and intensity, is indicated 
by the well-bedded character of the tuff and the alternation of finer and 
1 Student's Manual of Geology , 2d edit. (1862), p. 523. 
2 Op. cit. p. 19. y Op. cit. p. 523. 
