53 
CHEMICAL NOTES ON LAKE DISTRICT ROCKS. 
_1.—THE ORDOVICIAN VOLCANIC SERIES. 
ALFRED HARKER, M.A., F.G.S., : 
St. John’s College, Cambridge. 
SOME years ago, being then engaged with my friend, Mr. J. E. ; 
Marr, upon the geological structure of the English Lake * 
District, | began a petrographical study of the lavas and tuffs ; 
of the Ordovician volcanic series, or ‘ Borrowdale Series,’ which 
constitutes the greater part of the ground in that area. My 
unfinished notes consist chiefly of descriptions based on a large 
suite of microscopical sections, and these could not with 
advantage be published. There are also, however, a number 
of determinations of silica-percentages, kindly made for us by 
chemical friends, and of specific gravities, taken with the hydro- 
Static balance by the present writer. T it is desirable to 
make public for the benefit of other costae who may ; 
occupied with the district in question hie it may be useful 
to bring together references to t data scattered 
through various papers already published, Oo taihes belonging to 
the volcanic series or to other rocks in the district, and these 
references are accordingly collected below. omplete analyses 
are not quoted, but their silica-percentages are given as the 
readiest means of identifying the analyses referred to, 
The present instalment deals with the Ordovician volcanic 
series only, and the remaining rocks will be treated in a second 
part. Those portions of the Eden valley and Teesdale and of 
the Sedbergh and Ingleton districts which consist of Lower 
Paleozoic rocks, are included with the Lake District as Heings in 
a geological sense appendices thereto. 
The late Mr. Clifton Ward published several complete 
analyses by Mr. J. Hughes, of which the silica-percentages _ ie 
are here reproduced.* Ward considered the intermediate group ; 
(andesites) to be the prevalent lavas of the district, and a like 
assertion has been made by myself in ‘ The Naturalist’ for 1891 
(p. 146); but Mr. Marr and I have since found that it is the 
basic group that has the widest distribution. There is little 
doubt that some of Ward’s ‘altered ashes’ are in reality lavas, 
*The first five from Quart. Journ. Geol. Soc., vol. xxxi., pp. 408 
_ 597, 1875; also in ‘ The antiga of the Northern Part of the English He 
District’ (Mem. Geol. Surv.), pp. 16, 18, 28, i The next three from 
Monthly Micro, Journ., vol, xvii., p. 246, 80%: 
February : 1899. 
