68 Physical Geography. 



brides, on the coast of the West Highlands, where ex- 

 ceedingly red Cambrian sandstones and conglomerates 

 lie quite unconformably on the Laurentian strata. 



While the Menevian and Lingula beds were being- 

 deposited I think it more than probable that the pre- 

 Cambrian continent still existed, for in the gritty strata 

 that form a large part of the Lingula flags, and in the 

 frequent presence of current marks (often called ripple- 

 marks), there are many signs that these strata were de- 

 posited in shallow water, and thus it would happen, 

 that during the time when these and the Tremadoc beds 

 were being formed, the whole area was undergoing a 

 process of slow sinking, into which sediments were being 

 constantly carried, just in proportion as the gradual de- 

 pression went on, so that, in the long run, what witli 

 the effects of sub-aerial degradation, and what with the 

 results of progressing submersion, the old pre-Cambrian 

 land of this neighbourhood finally was buried and 

 disappeared. 



