36 JOANNES RASMUSSEN 



sequence. Likewise, it must be assumed that during the following stage, the 

 volcanism was more localized along the old fissures, respresented by the numer- 

 ous necks which are visible in cross- as well as longitudinal sections in coastal 

 profiles along the straits running NW.-SE. between the northern islands. 



The basalts in the Upper Basalt sequence display far greater variation 

 from bed to bed than do those of the Lower Basalt sequence. The following 

 main types occur: (1) dense, dark basalts without phenocrysts; (2) plagioclase- 

 porphyritic, grayish basalts with characteristic subtypes; (3) olivine basalts, 

 varying from ordinary olivine basalts to oceanities. All transitions between 

 these main types occur. 



While the thickness of the Lower Basalt sequence is about 1000 m, the 

 Upper sequence is considered to be about 2000 m, so that the whole Faeroic 

 sequence will be about 3000 m. However, in the geologic mapping work it has 

 proved justified and adquate to divide the Upper Basalt sequence into a 

 Lower and an Upper zone. In the Lower zone, comprising a httle more than 

 two-thirds of the sequence, the individual lava flows are generally of slight 

 thickness, often 1 to 2 m or less; however, beds of somewhat greater thickness 

 occur. The very thin lava flows, about 20 to 30 cm thick, appear frequently in 

 large numbers and may be explained as having run out through breaks in 

 thicker lava layers. Tuff" layers are very uncommon in this zone, and the 

 individual flows are usually separated by porous inter-zones and distinct 

 ropy-lava surfaces. Therefore, it must be assumed that the whole zone was 

 formed by a steady, continuous volcanic activity. In the Upper zone, com- 

 prising barely one-third of the Upper Basalt sequence, the individual flows are 

 usually about 1 m thick, and tuff" layers are common between the individual beds. 



The boundary between the two zones is usually distinct in the field and 

 clearly expressed in the topography. The Lower zone is exposed on the 

 northern part of Suduroy, on Vagar and on the northern part of Streymoy, 

 whereas it ispartlycoveredbythe Upper zone on the southern part of Streymoy, 

 Eysturoy, and the northern islands, except Fugloy and Svinoy where only the 

 Upper zone prevails. 



After the basalt plateau was completed, unequal withdrawal of the sub- 

 stratum resulted in readjustment movements which led to the formation of 

 fracture fines (master joints). Further readjustment movements along the 

 same lines of fractures results in "lamellae zones" which traversed the whole 

 sequence. Subsequently we have basaltic intrusions in these "lameflae zones" 

 and in other zones of weakness in the plateau. 



INTRUSIVES 



Intrusive formations occur as (1) irregular intrusive formations; (2)sills; and 

 (3) dykes. 



The dykes are intruded in the above "lamellae zones" and traverse the 

 entire plateau. The two other intrusion forms, irregular intrusive formations 



