CHAP. XIII 
THE LAKE DISTRICT 
227 
miles away, threw out only stones and dust, hut continued their intermittent 
explosions until they had strewn the sea-hottom with detritus to a depth of 
many hundred feet. 
There is yet another feature of interest in this independent group of 
submarine vents in Anglesey. Their operations appear to have begun 
before the earliest eruptions of the Bala volcanoes in Caernarvonshire. Their 
first beginnings may, indeed, have been cf)eval with the explosions that 
produced the older Arenig tuffs of Merionethshire ; their latest discharges 
were possibly the last manifestations of volcanic energy in MAles. They 
seeni thus to In’idge over the vast interval from Tremadoc to Upper Bala, 
possibly even to Tapper Silurian time. But we may, perhaps, connect them 
with the still earlier period of Cambrian volcanism. 1 have referred to the 
evidence which appears to show that the vents whence the lavas and tufls of 
Moel Trefan and Llyn I’adarn were erupted gradually moved northwards, and 
continued in eruption until after the beginning of the deposition of the black 
slates that are generally regarded as Arenig. The Anglesey tuffs and breccias 
may thus be looked upon as evidence of a still further shifting of the active 
orifices northward. In tins view, while the Aran and Cader Idris volcanoes 
broke out in Upper Cambrian and continued through Arenig time, and the 
Snowdonian group was confined to Bala time, a line of vents opened to the 
north-west in the Cambrian period before the epoch of the Llanberis slates, 
and, dying out in the south, continued to manifest a minor degree of energy, 
frec[uently discharging fragmental materials, but no lava, over the sea- 
bottom, until, towards the close of the Bala period, possibly even in Upper 
Silurian time, the}- finally became extinct. 
vi. THK VOLCANOES OF THE LAKE DISTKICT (ARENIG TO CLOSE 
OF BALA period) 
From the time of the appearance of Sedgwick’s classic letters to Words- 
worth, no volcanic area of Britain has probably been so well known in a 
general sense to the ordinary travelling public as the district of the English 
Lakes. Many geologists have since then visited the ground, and not a few 
of them have published additions to our knowledge respecting what is now 
known as the Borrowdale Volcanic Series. The most elaborate and detailed 
account of any part of it is that given by the late Mr. J. C. Ward in the 
Geological Sii'cvey Memoirs, wherein he embodied the results of his minute 
investigation and mapping of the northern portion of the district. Notices 
of the petrography of some of the more interesting rocks have subsequently 
been published by Mr. llutley, 1‘rofessor Bonney, Mr. Harker, Mr. Marr, 
Mr. Hutchings and others. But up to the present time no complete 
memoir on the volcanic geology of the Lake District as a whole has 
1 .Sheet 101 S.E. of the Geological Survey of England and Wales and Explanation illustrating 
the same; and paper.s by him in Quart. Journ. ffeol. Soc. vols. xxxi. xxxii. (1875-76). See also 
llessrs. Aveline and Hughes, Mem. Geol. Survey, Sheet 98 N.E. (Kendal, Sedbergh, etc.). 
