P.G. H. Boswell—Quantitative Methods in Stratigraphy. 168 
pietre verdi with each other ; their stratiform, if not actually stratified, 
character in relation to the sedimentary rocks, and their frequent 
wedges and lenticular intercalations in the latter—all these phenomena 
on a large scale still present an intricate problem to which I shall 
refer in the descriptive sequel of the present paper.’ The problem . 
of the age of the pietre verdi in relation to the older rocks is, of 
course, rendered more difficult by the obliteration in the latter of 
organic remains through the ceaseless action of metamorphism past 
and present, or, in the words of Gastaldi: ‘‘ while Nature gives us on 
this Karth myriads of living species, she with relentless hand destroys 
all trace of former life elowne 
(To be concluded in our next number.) 
TV.—Tuer Apprication or PrerrotogicaL AND Quantirative Mrrnops 
TO SrraTIGRAPHY. 
By P. G. H. BOSWELL, A.R.C.Sc., D.I.C., F.G.S., Imperial College, 
London, S.W. 
(Concluded from March Number, p. 111.) 
LTHOUGH detrital mineral work is as yet initsinfancy, sufficient 
has been accomplished to show that we may look to it with 
success for indications of changes of drainage direction, evidences of 
denudation by reversal of the order of respective miner al assemblages 
from a sequence of rocks,? and generally for information regarding 
details of paleogeography. Professor A. de Lapparent referred to 
Professor L. Cayeux’s work as proving the proximity of land, com- 
posed of primary rocks, to Lille in Landénian times. Dr. H. H. 
Thomas was able to demonstrate the change in source, and therefore 
in direction of drainage, of the river-borne heavy minerals in the 
Bunter sandstones of South Devon,‘ the occurrence of garnets and 
staurolite being especially significant. Dr. T. O. Bosworth, in some 
preliminary work upon the detrital minerals of the Carboniferous 
Sandstone of the Midland Valley of Scotland, was led to the conclusion, 
partly by the respective presence and absence of garnets, that the 
beds could be divided into a series of great lenticular masses of 
sediment introduced from directions varying from north and north- 
west to north-east, east, and south.° Mr. W. R. Smellie has discussed 
in rather more detail the origin of the minerals in the Upper Red 
Barren Measures of the Glasgow Basin, the drainage having been 
_ from the west or north-west.® As a result of the study of the Tertiary 
sediments of Hast Anglia, the writer has been able to prove that the 
1 Professor Bonney has described an instructive case of conversion of green- 
stone into schist on a small scale in the Bernina region, Q.J.G.S., 1894, 
p. 279 et seq. 
2 This idea was suggested for contained boulders by Professor Charles 
Lapworth in connexion with the Carboniferous conglomerates of Halesowen in 
Worcestershire. 
3 Traité de Géologie, 5th ed., vol. iii, p. 1492, 1906. 
4 Q.5.G.S., vol. lviii, p. 620 (Sand of Bunter Pebble- bed), 1902; vol. Ixy, 
p. 229 (New Red Sandstone), 1909. 
° Proc. Geol. Assoc., vol. xxiv, p. 57, 1913. 
§ Trans. Geol. Soe. Glasgow, volt XIV, Pala Glel owe: 
