1921. No. ir. THE STRANDFLAT AND ISOSTASV. I29 



X. THE STRANDFLAT OF NORTHERN NORWAY. 



Helgeland. 



The straiidflat is very conspicuous and extremely well-developed 

 along the coast of Helgeland between \'ikten and \'est Fjord. It consists 

 partly of an as a rule sharply marked plane or planes extending over 

 the hundreds of low islands and peninsulas, and to a still greater extent 

 of very flat submerged platforms with thousands of skerries, rocks, and 

 shoals. It has an average breadth of 40 to 45 kilometres as stated by 

 J. H. L. A'ogt [1900]. In some places it may even be 50 kilometres wide, 

 or more, from the steep mountain sides on the mainland to the cuter edg^ 

 of the submerged platform out to sea at less than 20 metres b,dow sea- 

 level. 



The strandfiat of Helgeland has been described by J. H. L. \^;)gt 

 [in 1900 and in 1907], and after him by several authors, especially Hog- 

 bom [19 13], Oxaal [1914], Sahlstrøm [1914], and Rekstad [19 15]. In the 

 two latter papers there are given some most illustrative pictures of the 

 strandfiat and the isolated mountains rising abruptly like 'stacks" above 

 its plane. The present writer has also previously [1904] described the 

 strandfiat along the coast of Helgeland. 



This coast has a very complex geological structure, and is built up 

 of a great variety of rocks. They are chiefly mica-schists, granites, voung 

 gneisses, lin:estone, gabbro, some svenite, and some serpentine. Th S2 

 rocks vary much in their power of resistance to erosion, the granites and 

 gabbros and also the serpentine (on Leka) and the gneisses are as a rule 



Fig. 113. Map of the coast of Helg-eland from Bindal Fjord to Donna Island. Scale i : 350,000. 

 Black areas on land are lower than 30 metres above sea-level. The dark hatching on land 

 indicates areas between 30 and 50 metres above sea-level. The light hatching in the sea 

 indicate submerged plateaus with depths less than 25 metres below sea-level. Isobaths are 

 drawn for every 50 metres of depth, i. e. for 50, 100, 150, 200, 250, &c. The black spots 

 Indicate rocks and skerries above sea-level. The small crosses indicate sunken rocks and 

 shoals, crosses zvith spots indicate rocks near sea-level, and (lotted areas shoals near sea- 

 level. The figures on the land and in the sea give the heights and depths in metres. 

 I Vega Island. II Sola Island. Ill Ulvingen Island. IV Hamnoi. V Tjotta Island. VI Alsten 

 Island. VII The mountains „Syv Søstre" (Seven Sistersl. VIII Heroi. IX Donna Island. 

 Vid.-Selsk. Skrifter. I. M.-N. KI. 1921. No. 11. 9 



