239 



FOLIATED ROCKS SIMILAR TO THE ABOVE IN COMPOSITION. 



I. II. III. IV. V. 



Si0 2 50-57 ... 48-30 ... 46'89 ... 46'57 ... 52'54 



A1 2 3 19-65 ... 17-04 ... 20-46 ... 19-50 ... 23'83 



Fe 2 3 1-46 ... 2-73 .. 2'19 ... 1'84 ... 2-44 



FeO 7-24 ... 9'50 ... 11-15 ... 12-80 ... 4*87 



MnO tr. ... tr. ... tr. ... (r. ... tr. 



CaO 7-47 ... 13-30 ... 8'37 ... 9'91 .. 7'89 



MgO 7-93 ... 6-18 ... 5-83 ... 3D3 ... 2'67 



Na 8 3-46 ... 2'01 ... 8'87 ... 3-50 ... 311 



K 2 1-08 ... -30 ... tr. ... -51 ... 1-95 



P 2 5 -12 ... tr. ... -31 ... -63 ... tr. 



FeS 2 tr. ... tr. ... tr. ... tr. 



H 2 -74 ... -74 ... -97 ... '88 ... -63 



99-72 100-10 100-04 100-07 99-93 



Sp. Gr. 2.89 8.03 3.03 3.02 2.89 



I. Greenish grey rock from a quarry in the village of Newlyn, near Penzance. 

 II. Bluish grey slaty " greenstone " two miles W. of Camborne. 



III. "Blue elvan " from Terrace about a mile and a half west of St. Stephen's Church. 



IV. Compact greyish "greenstone " showing tendency to break into plates ; North Hu el Rose. 

 V. Green slaty rock from St. Clcer Down. 



FOLIATED BASIC HORNBLENDE-ROCKS. 



I. II. III. IV. V. 



Si0 2 ... 37-44 ... 85-58 ... 39'20 ... 36'57 ... 37'72 



A1 2 3 ... 16-82 ... 21-14 ... 16-22 ... 15'34 ... 17'19 



Fe 2 3 ... 7-33 ... 14-74 ... 4'82 ... 7'57 ... 7'75 



FeO ... 14-75 ... 10-32 ... 16-88 ... 14-84 ... 15'81 



MnO ... tr. ... tr. ... ... tr. ... -43 



CaO ... 12-83 ... 9-20 ... 10.70 ... 12*58 ... 14-00 



MgO ... 6-06 ... 2-78 ... 6-56 ... 5'98 ... 8'41 



Na 2 ... 1-85 ... 2-11 ... 1-45 ... 2'99 ... 1-06 



K 2 ... 1-50 ... -95 ... 2-69 ... 1-44 ... 1-02 



PA ... -27 ... tr. ... -74 ... -68 ... -41 



FeS 2 ... -23 ... tr. ... ... ... tr. 



H 2 ... 1-31 2-93 1-40 1'74 1-39 



99-89 99-75 99-66 99'73 100-19 



Sp. Gr. 3.29 3.15 3.26 3.28 3.35 



I. Paul Hill, Paul, near Penzance. 



II. Rose Hill, Castle Horneck, near Penzance. 

 III. Chyandower, Penzance. 

 IV Rosemorran Gulval, near Penzance. 



V. Pendower Cove, near St. Ives. 



The more important facts described above may be summarized as 

 follows : 



(1) Basic lavas and tuffs occur in association with Devonian strata. 



(2) Rocks of the dolerite-type occur in a comparatively unmeta- 



