CHAP. II.] CAMBRIAN PERIOD. 25 



by continued subsidence, which broadened the sea-spaces 

 at the expense of the land. 



In dealing specially with the geographical conditions of 

 the British area, I have sought the assistance of Dr. Calla- 

 way, whose studies of the Cambrian rocks are well known, 

 and he has kindly furnished me with an outline of such in- 

 ferences as he thinks it is safe to draw in the present state 

 of our knowledge. These are as follows : 



" The ideal reconstruction of the geography of any past 

 epoch is always a rather speculative task, but it becomes 

 especially difficult when we revert to a period so ancient as 

 that of the Lower Cambrian or Longmyndian. We can 

 learn little about tracts which are covered by post-Cam- 

 brian deposits, and the deep borings of the south-east of 

 England give us no help. We can, however, determine 

 the approximate position of some of the land masses which 

 rose amidst the waves of the Longmyndian sea. 



"The groups of volcanoes which in later Archaean times 

 had spread out their lavas and ashes over so large a part 

 of England and Wales were extinct at the commencement 

 of the Cambrian period, but it would seem that several 

 mountain chains, some of them crowned like the Andes or 

 the Eocky Mountains by numerous volcanic cones, stood 

 above the waves. Dry land probably extended over what 

 are now the counties of Shropshire, Staffordshire, Leicester- 

 shire, Warwickshire, and Worcestershire, at least as far 

 south as Malvern, but how far this land stretched to the 

 north, east, and south, we have no means of knowing ; it 

 can only be said that analogy points to its having had a 

 considerable north-east and south-west extension. 



" The preponderance of coarse sandstones indicates a 

 rapid submergence of the neighbouring land, and the basal 

 conglomerates in Wales indicate the gradual advance of 

 the waves over a sinking shore. The rapid thinning-out of 

 the Cambrian strata toward the west suggests that in the 



