106 STRATIGKAPHICAL GEOLOGY 



In the western areas arenaceous material prevails not only in 

 the Lower Cambrian, but also in the Middle and Upper divisions, 

 for in North Wales a large part of the Lingula Flag Series consists 

 of flagstones which become coarse quartzose grits as they are 

 followed through Carnarvonshire. On the other hand, in Scotland, 

 Sweden, and Russia sandstone is practically confined to the lowest 

 stage, all the higher portions of the system consisting of limestone 

 and shale. 



As the Swedish geologist Linnarsson wrote in 1876, "The facts 

 rather tend to show that most of the Swedish Cambrian rocks were 

 deposited in a deeper sea and farther from land than the British." 

 He points out that the small thickness of the Olenus Beds over such 

 a large area in Sweden can only be explained on this view, for they 

 are so thin compared with the Liugula flags of Wales that the 

 rate at which sediment was accumulated in Wales must have been 

 fifty or sixty times as rapid as it was in Sweden. This must have 

 been due to the much greater proximity of land, while all the facts 

 connected with the Upper Cambrians of Sweden lead us to infer 

 that they were deposited in a deep sea and far from land. 



We may therefore conclude that the greater part of the 

 materials forming the Cambrian deposits in France, Wales, and 

 England were derived from lands which lay to the west of France 

 and to the north-west of Wales. That which lay west of France 

 and south-west of Wales was probably part of a large land-area or 

 continent, occupying part of what is now the Atlantic Ocean, and 

 terminating eastward in a promontory which included the northern 

 part of Brittany during early Cambrian time, but was submerged 

 in the later part of the period. 



The land to the north-west of Wales may have been an island 

 or another promontory of the Atlantic continent. It included 

 Anglesey and probably stretched across the Irish Sea into 

 Ireland, but until more is known about the structure of the north 

 of Ireland it is impossible to say how far it reached in that 

 direction. 



Open sea seems to have extended across the North Atlantic 

 region from America to the north of Scotland with circumpolar or 

 Arctic land again to the north of it, for it is only in this way that 

 the American character of the Scottish Cambrian fauna can be 

 satisfactorily accounted for (see The Building of the British Isles, 

 3rd edition, p. 63). This northern sea may not have been very 

 deep, but its waters must have become deep enough and clear 

 enough in Middle Cambrian time for the formation of limestone, 

 and in the Scottish limestones there is evidence that the accumula- 

 tion of shell-debris and calcareous matter went on very slowly ; for 



