29 



Disse mikroskopiske Forhold minder unægtelig om 

 Eruptiver, som bliver finkornede paa sine Grænser og 

 sender finkornede Forgreninger ud i de omgivende Berg- 

 arter. Hvorvidt her foreligger et Afkjølingsfænomen er 

 dog tvivlsomt; maaske Olivinen allerede ved sin Udkrystal- 

 lisation har paavirket Grundmassen, saa den i dens umid- 

 delbare Nærhed har stivnet hurtigere. Lignende Forhold 

 som disse ved Olivinen beskrevne iagttages, om end mindre 

 karakteristisk, ved de udskilte Plagioklas- og Augitkrystaller. 



Haandstykket No. 8 er porøst, af en forholdsvis lys, 

 rodliggraa Farve og indeholder udskilte •Augitkrystaller. Un- 

 der MikroskoiJ ser man, at Bergarten, som er forholdsvis 

 lidet grovkornet og lidet rig paa mindre Augitindivider, 

 indeholder en hel Del Olivin. Dennes Individer udhæver sig 

 ikke synderlig i Størrelse fremfor de øvrige Bestanddele; 

 den er ikke som i de foregaaende Tilfælde frisk, men un- 

 derkastet en begyndende Serpentinisering ledsaget af Ud- 

 skillelse af Jernoxyd, som er det, der gjør Bergarten rødlig. 

 Slaggeagtigt Glas er temmelig rigelig tilstede. Nogle lange 

 fine Naale i Feldspaten formodes at være Apatit. 



Haandstykket Xo. 1 udmærker sig fra de beskrevne 

 mikroskopisk derved at det ingen porfyrisk udskilte Feld- 

 spatkry staller indeholder, men derimod en Mængde smukke 

 gulagtiggrønne 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 være udkrystalliseret etter en anden Typus end foregaa- 

 ende. benuerkes hyppig det som Picotit tydede Mineral. Den 

 mørke Jernerts er tilstede ikke alene i rundagtige Korn, 

 men ogsaa i stavformede Legemer. Disse forekommer som 

 Regel nær Olivinkrystallerne og har en bestemt Stilling til 

 disse, uanseet Bergartens øvrige 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 uemlig lodret mod deres bedste Gjen- 

 nemgangsretning. Man faar Indtrykket af. at Bergartens 

 først udskilte Bestanddele, Olivinen og Jernertsen, i den 

 endnu plastiske Masse har ordnet sig i et bestemt Forhold 

 indbyrdes. 



These microscopic details are undeniably suggestive 

 ol' eruptive rocks that exhibit a tine granulation at their 

 limits and send fortb finely granulated ramifications. Whether 

 we have liere 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 barden sooner. A similar feature, 

 tbough 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 :t coarse granulation and exhibits but few 

 partieles of augite. contains a good deal of olivine. The 

 prystals 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 yellowish-green crystals of olivine, measuring up to 

 0.5 cm. 



Yiewed 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, butalso 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 jærpendicular 

 to the most perfect cleavage. The first-formed consti- 

 tuents of the rock, olivine and iron ore, would appear to 

 have tåken up a definite position one towards the other 

 while the surrounding mass was vet plastic. 



Olivinkrystal i Basalt. — 



Den i stavformede Legemer forekommende Jernerts har en 

 bestemt Stilling i Forhold til Olivinkrystallen. Tegnet ved 360 

 Gawres Forstørrelse. 



A Crystal of Olivine in Basalt. 



The iron ore occm - ring as rod-shaped corpuscles has a definite 

 position towards the crystal of olivine. — Microscope magnifyin» len 

 diameters. 



