29 Disse mikroskopiske Forhold minder untegtelig om Eruptiver, som bliver iinkornede paa sine Graenser og sender finkornede Forgreninger ud i de omgivende Berg- arter. Hvorvidt her foreligger et Afkjplingsfsenomen er dog tvivlsomt; maaske Olivinen aJlerede ved sin Udkrystal- lisation har paavirket Grundmassen, saa den i dens umid- delbare Naerhed bar stivnet hurtigere. Lignende Forhold som disse ved Olivinen beskrevne iagttages, om end mindre karakteristisk, ved de udskilte Plagioklas- og Augitkrystaller. Haandstykket No. 8 er porpst, af en forholdsvis lys, rpdliggraa Farve og indeliolder udskilte Augitkrystaller. Un- der Mikroskop ser man, at Bergarten, som er forholdsvis lidet grovkornet og lidet rig paa mindre Augitindivider, indeholder en hel Del Olivin. Dermes Individer udhsever sig ikke synderlig i Stprrelse fremfor de pvrige Bestanddele; den er ikke som i de foregaaende Tilfaelde frisk, men un- derkastet en begyndende Serpentinisering ledsaget af Ud- skillelse af Jernoxyd, som er det, der gjpr Bergarten rpdlig. Slaggeagtigt Glas er temmelig rigelig tilstede. Nogle lange fine Naale i Feldspaten formodes at vsere Apatit. Haandstykket No. 1 udmaerker sig fra de beskrevne makroskopisk derved at det ingen porfyrisk udskilte Feld- spatkrystaller indebolder, men derimod en Maengde smukke gulagtiggrpnne Olivinkrystaller, som er indtil 0.5 cm. store. Under Mikroskopet ser man, at Hulrummene gjerne er omgivne med en Zone af Glas. I Olivinen, der synes at vasre udkrystalliseret efter en anden Typus end foregaa- ende, bemaerkes liyppig det som Picotit tydede Mineral. Den morke Jernerts er tilstede ikke alene i rundagtige Korn, men ogsaa i stavformede Legemer. Disse forekommer som Regel mer Olivinkrystallerne og har en bestemt Stilling til disse, uanseet Bergartens pvrige paa kryds og tvers lig- gende Bestanddele. De staar, saavidt jeg har kunnet iagt- tage det, lodret mod Olivinernes Hovedakse, parallelt deres lange Biakse; de staar nemlig lodret mod deres bedste Gjen- nemgangsretning. Man faar Indtrykket af, at Bergartens forst udskilte Bestanddele, Olivinen og Jernertsen, i den endnu plastiske Masse har ordnet sig i et bestemt Forhold indbyrdes. These microscopic details are undeniably suggestive of eruptive rocks that exhibit a fine granulation at their limits and send forth finely granulated ramifications. Whether we have here the result of some cooling process is doubtful; possibly, the olivine acted in the course of its crystallisation upon the basic substance, thereby causing the latter in its immediate vicinity to harden sooner. A similar feature, though less characteristic than in the olivine, distinguishes the imbedded crystals of plagioclase and augite. Specimen No. 8 is porous, of a lightish ruddy- grey colour, and contains imbedded crystals of augite. Viewed under the microscope, this rock, which, compara- tively, has not a coarse granulation and exhibits but few particles of augite, contains a good deal of olivine. The crystals of the latter substance are not very large as com- pared with its other constituents; the olivine is not as in the foregoing specimens undecomposed, but exhibits distinct traces of serpentinisation, along with the formation of oxide of iron. This it is which gives a red colour to the rock. Slaggy glass occurs in comparative abundance. A few long thin crystals in the feldspar would appear to be apatite. Specimen No. 1 is distinguished macroscopically from those described above, by its not containing imbedded crys- tals of feldspar; it exhibits, however, an abundance of beau- tiful yellowisli-green crystals of olivine, measuring up to 0.5 cm. Viewed under the microscope, the hollow cavities are found to be encompassed by a zone of glass. The olivine exhibits a type of crystallisation different to that observed in the other specimens, and contains a greater proportion of picotite than usual. The dark iron ore occurs not only in roundish grains, but also in rod-shaped corpuscles. These corpuscles are as a rule observed in immediate proximity to the crystals of olivine and have a definite position towards them, irrespective of the other constituents of the rock, that run in all directions. They are placed, so far as I could determine, perpendicular to the vertical axis of the crys- tals, and parallel to the macrodiagonal, being perpendicular to the most perfect cleavage. The first-formed consti- tuents of the rock, olivine and iron ore, would appear to have taken up a definite position one towards the other while the surrounding mass was yet plastic. Olivinkrystal i Basalt. — A Crystal of Olivine in Basalt. Den i stavformede Legemer forekommende Jernerts har en jj The iron ore occurring as rod-shaped corpuscles has a definite bestemt Stilling i Forhold til Olivinkrystallen. Tegnet ved 360 position towards the crystal of olivine. — Microscope magnifying 300 Ganges Forstprrelse. II diameters.

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