284 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
hundred analyses of igneous rocks from all parts of the globe and 
made by many analysts of various nationalities. These are shown, 
respectively, in columns I and II of Table I, only the more important 
constituents being considered and the whole being reduced to 100 per 
cent. Harker’s estimates are omitted, but in general they conform 
to those here presented. 
TABLE I.—Average composition of igneous rocks, 
United II. Gonmpiee IV 
| States, sees average, Clarke, 
Crarke; ton, 1903. Clarke, | 1904. 
STO) i ae en 60. 48 BE78)|" - /SOSSTA DINO Sore-e- eee mente eae | 47.09 
NORE a ie UR ane 15.17 15. 67 159020 AIGie et ee a Patent 28. 23 
TOES O MP eas acy eee ae a 2. 61 3.31 OCH eee eam ec 7.99 
TPE ee ay Pas ge ae Me 3.44 3.84 COE | |i ee eee ee 2. 4. 46 
IMPOR ess te ccn scecenaes 4.10 3.81 4. 06 Caseteeaws sient cee nebo 3. 43 
(CRYO ae. aR nt Sere 4.84 5.18 BN 79 An Nat he a 2. 58 
Nas O ROS etn te se act 3. 43 3.88 S¥SO lpia tts 2e ete here 2. 46 
KOA LE eek eke ee 2.96 3.13 DIGS Wh WKerde tes nese eae 2. 44 
eG (UIOEP) ek cece 1. 48 1. 42 A AbH esl | Pie ee taxtees nn. eee . 43 
Eig O) (U1O2=)tc.ceesece cece 41 .36 Mage ail EIee Abts Pat eas Ee 17 
UO sacocacdsacpecscdecsetbe St? 1.03 aie) Cie eh eee 14 — 
le ORs daceas shane bussseooctar . 26 nays - 26 Pee iancecesee re naueeeee Aili 
MnO Mestad one .10 .22 S10) WI ESceeewes cee eee “it 
(OO see Seo nACD ASO HORE ER OeEad Beronaa coed badadacacacr <2 — val || PBB oasecrccenate ceo eerie . 089 
ee DAE See an. GES eee Sepa Eee ee Lae AMIN Ae Seer oe eer 084 
1S OSS GOR SCOR EEE See Henn HA neceeencere aaconsesasoc sili | ( 0) eae sear a -07 — 
Cl see ee SI A on SAL Sas ee TOZS/llluGr ete ee eee tae .034 
(OHO ocd Gan tanec na cbbeae Rotel oncaaesl beeposaasane O5==9)l)| (Crease. accep aere oe aeeeeee - 034— 
SO eres Zeid sn, epee dee Le Ae SI E (0 Saran 7 Aces yea uk es oe . 026— 
(5 (CT ee SU, Bade er a S| ee a See dP) Wee hd a Oe 4 Ne Rae ae seen ee [oz 
INTO ett Pe hte Seah laine lng es RN p(s Salli oe Oa oc Seer cre 02 + 
WO ste recis Sone neonate mere re ee ere al (Npeenae ek Sart a . 03— AY ENR et ae eS Se aL I Oe -02 — 
RE ae oe Sake SA See Cae Pe Oa. AiO | a ie epee eet ie Pa aP 01 
lO RON a a sce a tS eee SHOT Se ae ae ee Bal AReBsaAaecne 01 
| 100. 00 100. 00 100. 00 100. 00 
It is evident that the two are very closely alike, the only noteworthy 
divergence being in the amount of silica. he higher figure in I 
may be ascribed in part, as pointed out by Clarke, to the inclusion of 
many separate silica determinations, which were undertaken on rocks 
comparatively high in this constituent; in part to the inclusion in the 
estimate of some analyses of siliceous gneisses and schists, rocks which 
were not regarded in my estimate; and probably in part to the fact 
that in Clarke’s estimate only rocks from the United States were 
considered. But notwithstanding the slight discrepancies and the 
uncertainty introduced by nonallowance for the disturbing factors 
mentioned above, the results of the two calculations are so concordant 
that we may feel a high degree of confidence in the belief that the 
