THE GREAT SCANDINAVIAN OVERTHRUST 411 



The criticisms have followed three main lines, (i) The post- 

 Silurian age of the schists and gneisses overlying the sediments 

 is still maintained by several Scandinavian geologists. (2) 

 The superposition of the older beds has been attributed by 

 Svenonius to complex overfolding ; he explained the succession 

 of the rocks in Norrbotten b}- contortions similar to those 

 formerly introduced in Swiss geology (fig. 6, after Svenonius). 

 (3) The invocation of numerous overthrusts instead of one vast 

 movement. 



The third hypothesis has been advanced by Dr. Holmquist, 

 from the evidence collected in his careful study of the districts 

 to the south of Tornetrask. He holds that instead of there 

 having been one vast overthrust, which in that area would 

 have to be thirty-five miles or more in width, there have 

 been many shorter overthrusts. The "Silurian" rocks have 

 been thus sandwiched between the crystalline rocks ; and, 



jv^vv 



s. E 



Fig. 6. — Section through Daunevarra, Lapland (after Svenonius, 1896). 



according to Dr. Holmquist, the tops of the folds sometimes 

 expand laterally beyond their impressed limbs, like an exag- 

 gerated Alpine fan. But these sections have been ridiculed 

 as " mushroom constructions " by Tornebohm, who holds to 

 his faith in one great movement.- Dr. Holmquist's view, 

 however, appears to be possible, and it has the recommen- 

 dation of making less tr3nng demands on the strength of the 

 rocks. The overthrust rock-masses are comparatively thin in 

 proportion to their extent, and it would appear very doubtful 

 whether they could have been thrust forward in a slab by 

 pressure applied thirty miles behind in the case of Lapland and 

 eighty miles distant in Jemtland. We are forbidden to appeal 



' F. Svenonius, " Om Berggrunden i Norrbottens Lan," Sz'er. Gcol. Undejsok. 

 Ajhandl. Ser. C, No. 126, 1892, pp. 37-41, and "Nigra Bidrag till belysning af 

 eruptivens betydelse for fjallbildningarna," Sver. Geol. Unders. Afharidl. Ser. C, 

 No. 161 (1896), pi. I. 



* A. E. Tornebohm, " Om Tornetrask-profilenstydning," Geol. For. Fork, vol. 

 XXV. (1903), pp. 83-92. 



