The Old Red Sandstone Volcanic Rocks of Shetland. by BN PEACH and J. HORNE, of the Geological Survey of Scotla
( 359 ) XXI.—The Old Red Sandstone Volcanic Rocks of Shetland. By B. N. PEACH and J. HORNE, of the Geological Survey of Scotland. (Plates XLV. and XLVI.) CONTENTS. PAGE Introduction, 359 5. Necks on Bressay and Noss, . 377 I. GEOLOGICAL STRUCTURE OP THE VOLCANIC 6. Summary of Events indicated by ROCKS, 361 Volcanic Phenomena of Shetland A. Contemporaneous Lavas and Tuffs, . 361 Old Red Sandstone, 378 1. Porphyritic Lavas and Tuffs of North- mavine, . .361 II. MICROSCOPIC CHARACTERS. 379 2. Diabase Lavas and Tuffs of Aithsting 1. Porphyrite LavasA and Sandsting, .... 364 2. Diabase Lavas, lBasic Rock8> . 379 3. Probable Horizon of the Lavas and 3. Intrusive Diabase | Tuffs of Aithsting and Sandsting, 365 Rocks, ' 4. Lava of the Holm of Melby, . 366 4. Intrusive Sheets— . 381 5. Bedded Lavas and Tuffs of Papa Rooeness Sheet, . 382 Stour, 366 Sandsting Sheet, . 382 6. Band of Tuff in Bressay, . 367 Papa Stour Sheet, . 382 B. Intrusive Igneous Bocks, .... 368 5. Dykes— Acidic Rocks. 3 83 1. Intrusive Sheet of Binary Granite Binary Granites . 383 in Northmavine, .... 368 and Quartz-fel- 2. Intrusive Sheet of Granite in Sand- sites, . 383 sting, 370 Rhyolites, . 384 3. Intrusive Sheet of Spherulitic Fel- Summary of Results, . 386 site in Papa Stour, . 371 4. Dykes— 373 APPENDIX.—Table of Chemical Analyses of a. Binary Granites, . 373 eight Specimens of Shetland Old Red 6. Quartz-felsites, . 373 Volcanic Rocks, by R. R. TATLOCK, c. Rhyolites, .... 374 F.R.S.E., 387 d. Diabase Rocks, . .376 Perhaps the most interesting feature connected with the Old Red Sandstone formation in Shetland is the evidence of prolonged volcanic activity in those northern isles.
[Show full text]