572 A. W. GRABAU LOWER ORDOVICIC FORMATION'S 



Cambric rather than Algonkian age. ISTo fossils have been found in this 

 rock so far, so that its age is problematical. But if Eothpletz has solved 

 the tectonics of the region correctly, it is most certainly Lower Paleozoic. 

 The Biri limestone is a mixture of calcilutites and calcarenites ; it is gen- 

 erally well stratified, and edgewise conglomerates, intraformational fold- 

 ing through slumping, as well as sun-cracks, appear in it, indicating 

 relatively shallow water conditions during accumulation, with intermit- 

 tent emergences. Ripple-marks were also observed by Walther on some 

 of the surfaces. 



The development of early Paleozoic rocks in a calcareous facies like 

 that of the Biri limestone in the northwestern part of the Scandinavian 

 land-mass, whence these thrust masses are derived, is the more remark- 

 able, since the sandy and shaly development of these strata in the south- 

 ern part of the peninsula, and even in the region in which these limestones 

 are now found shows a distinctly northward overlap, a condition of occur- 

 rence which presupposes the existence of a land-mass in the neighborhood. 

 This land-mass must have lain between the area of the marine trans- 

 gression from the south and the region of deposition of the Biri limestone. 

 This limestone might be regarded as deposited in a great area of inland 

 waters, but, as Walther rightly remarks, its extent and the absence of 

 silicious elastics in it form a difficult problem on the basis of such an 

 assumption. To be sure, the maximum thickness today is only 170 to 

 200 meters, but that is not its greatest original thickness, for its relation 

 to the higher beds is in nowise definitely ascertained. 



A more rational explanation of the origin of this limestone Avould seem 

 to be that its accumulation took place in the waters of a sea lying to the 

 north of the Scandinavian land-mass, formed at a time when the Atlantic 

 Ocean transgressed across part of the same mass from the south. This 

 would give these limestones and the underlying sandstones the same rela- 

 tionship, to the Cambro-Ordovicic sandstones and shales in southern 

 Sweden that the Eriboll quartzite and Durness limestone series have to 

 the Lower Cambric sands and to the Tremacloc and Arenig beds of the 

 south of Britain. On this basis, the Biri limestone would have to be 

 considered the eastward continuation of the Durness limestone, just as 

 the Cambric and early Ordovicic beds of Sweden are the eastward con- 

 tinuation of the sands and shales of Wales and England formed during 

 the same period. Whether the Biri limestone represents only the Lower 

 Cambric portion of the Durness — that is, the G-hrudaidh and Eilean Dubh 

 groups — or whether a part of the Beekmantown facies is also included, 

 must remain an unsolved question until fossils are discovered. Certainly 

 there is nothing in the physical character of the Biri limestone which 



