47 



water-worn, thougli angular fragments, of the ferrugineous 

 nodules so characteristic of the Windmill Hill beds ; the 

 beaches all along the Tamar are principally composed of them. 

 Some of these ridges and terraces are about 100 feet above 

 the present river. 



It is very probable that the water flowing over the barrier 

 which had dammed up the old valley and river course into a 

 lake, would during this period rapidly cut and wear out a new 

 channel for itself; and that to the gradual deepening of 

 this channel, and the consequent shallowing of the upper 

 lake levels, we mav ascribe the scoonine^ out of mnsf. nf 



{MB. JOHNSTON'S TAPER.) 



ERRATA. 



embedded in scoriae. 

 Fig 28. — Reed-like impression. Windmill Hill. 



Note.— All leaf figures are drawn at from half to one-third natural size. 



