chap. XXIX 
THE DERBYSHIRE TOADSTONES 
21 
coarser layers. Large blocks of lava, two feet or more in diameter, may 
mark some of the more vigorous paroxysms of the vents, while the usual fine 
granular nature of the tuff may point to the prevailing uniformity and less 
violent character of the eruptions. Bands of tuff 7 0 leet or more in thick- 
ness, without the intercalation of any limestone or other non-volcanic inter- 
calation, point to episodes of such continued volcanic activity that the ordinary 
sedimentation of the sea-bottom was interrupted, or at least masked, by the 
abundant fall of dust and stones. 
One of the best exposures of such intercalations of bedded tuffs was 
Pointed out to me by Mr. Bemrose, immediately to the east of the village oi 
Litton. The matrix is crowded with the usual minutely vesicular glassy 
lapilli, and encloses fragments of diabase of all sizes, up to blocks more than 
a foot in diameter. The rock is well stratified, and the layers of coarse 
and fine detritus pass beneath a group of limestone beds. The actual 
junction is concealed under the roadway, but only two or three feet of rock 
cannot he seen. The lowest visible layer of limestone is nodular and contains 
decayed bluish fragments which may be volcanic lapilli. Immediately above 
the lower limestones the calcareous bands become richly fossiliferous. .Some 
°t their layers consist mainly of large bunches of coral ; others are crowded 
with cup-corals, or are made up mainly of crinoids with abundant brachiopods, 
polyzoa, lamellibranclis, gasteropods and occasional fish -teeth. This re- 
markable profusion of marine life is interesting inasmuch as it succeeds 
immediately the band of volcanic ash. 
Another well-marked zone of tuff, with no traceable accompaniment of 
lava, has already been referred to as connected with the Grangemill vents, 
lu this case also, the limestone that lies directly upon the volcanic material 
m rather impure and nodular in character. The tuft itsell is well bedded, 
Perhaps from 70 to 100 feet thick and dips underneath an overlying series 
°f marine limestones. 
I did not observe thin partings of tuff and disseminated volcanic lapilli 
among the limestones, such as are so marked in the Lower Carboniferous 
formations of West Lothian, and in the Limerick basin, to be described in the 
following chapter. But a diligent search might discover examples ol them, 
‘ ln d thus prove that, besides the more prolonged and continuous eruptions 
that produced the thick bands of tuff, there were occasional feeble and inter- 
mittent explosions during the accumulation of the thick sheets of limestone. 
‘ °me of the layers of “ red clay ” observed in shafts sunk lor mining purposes 
niay perhaps represent such spasmodic discharges of fine fragmental material. 
m the sills. — No attempt has yet been made to determine whether and 
fo what extent the toadstone bands include true intrusive sheets. My own 
a fot examination of the ground does not warrant me in making any positive 
statement on this subject. I can hardly doubt, however, that some, perhaps 
I10t a few, of the toadstone bands are really sills. In the accounts of these 
r,,c ks contained in the mining records a distinction, as already remarked, 
appears to have been generally drawn between “ toadstone and “ blackstone. 
fLe latter term is applied to the black, fresh, more coarsely crystalline, and 
