T. Crook—Titaniferous Volcanic Rocks. 161 
rutile and ilmenite both occur as intergrowths with magnetite, and 
it is not at all uncommon for titaniferous magnetite to leave a residue 
of rutile when crushed and leached with strong hot hydrochloric acid. 
Therefore, unless it can be proved that ilmenite and rutile were absent, 
Dr. Washington’s analysis of the above-mentioned rock residue does 
not prove that the titanium dioxide was present as titaniferous augite. 
As regards the Linosa hornblende, which ‘‘ yielded as much as 8°47 
per cent. of titanium-dioxide,” we need evidence that no inclusions of 
ilmenite, etc., were present in the crystal analysed. Indeed, some of 
the evidence so far adduced by various workers to stipport the view 
that titanium enters vitally and in any serious quantity into the 
composition of ordinary ferromagnesian minerals, is not at all 
convincing in its character. 
Again, on page 73 (loc. cit.) Dr. Washington makes the following 
statement concerning the Western Mediterranean basalts and their 
titanium content: ‘‘ Of the minor constituents, titanium-dioxide is the 
most notable. This constituent is present in every case in very large 
amounts: large, that is, for this substance, the average amount of 
which in igneous rocks is 1 per cent. or less. Indeed, the higher 
figures found in the table are unparalleled elsewhere, except in 
titaniferous ores.” 
Now considering the fact that titanium dioxide is more abundant in 
basic than in acid igneous rocks, we may reasonably contend that the 
Western Mediterranean basalts should be compared with other 
basalts, rather than with rocks in general, if we wish to understand 
the correct bearing of any peculiarity which they may exhibit with 
respect to their titanium content. While it may be true that igneous 
rocks in general do not average more than 1 per cent. of titanium 
' dioxide, this statement is not true of the salfemane class, and it 
is still less true of certain yet more basic types. e 
In order to test this point fairly, let us take the analyses of the 
rocks of the salfemane class given in Dr. Washington’s valuable 
compilation of rock analyses.' Of the 230 superior analyses of 
salfemanes there given, in which titanium dioxide was actually 
estimated, these rocks show a range from 0:03 to 6:18 per cent. of 
that oxide, with an average of about 1°67 per cent. Of these 230 
salfemanes, 75 have more than 2 per cent. of titanium dioxide, 33’have 
over 3 per cent., while 16 have more than 4 per cent., and several 
have more than 5 per cent. 
Further, Dr. Washington gives in his list of superior analyses, five 
taken from the results obtained by Grubenmann for the melilite- 
basalts of Baden. Of these five analyses, one is included in the 
salfemanes and four in the dofemanes; they range from 4°79 to 8°85 
per cent. of titanium dioxide. 
Instances could be multiplied to show the abundance of titanium in 
certain basic igneous rocks which are not ‘titaniferous ores.’ Indeed, 
the abundance of titaniferous ores themselves as segregations in igneous 
rocks is sufficient to make any one pause before giving assent to 
Dr. Washington’s proposition, that the percentage of titanium dioxide 
1 « Chemical Analyses of Igneous Rocks’’: Professional Paper, No. 14, U.S. Geol. 
Survey, 1903. 
DECADE V.—VOL. IV.—NO. IV. 11 
