100 Dr. Wright on the Geology of the Isle of Wight. 



tions of physical conditions from river or lake to estuary and sea 

 prevailed. 



2nd. That the upper lacustrine strata exhibit such alternations, 

 is shown by bed No. 2, but sail more clearly by the section at 

 llampstead Cliff, which belongs to this group. The consider- 

 ation of its beds does not fall within the limits of our section, 

 belonging as they do to a higher zone in the upper lacustrine 

 series. The lower lacustrine beds present similar phenomena. 



3rd. That the estuary conditions more especially prevailed 

 before and after the deposition of the intercalated marine bed. 



4th. That the upper marine indicates a period in the straggle 

 between sea and lake, when the former obtained for a time the 

 supremacy : the marine shells and sharks' teeth it contains prove 

 this condition. 



5th. The white and yellow sands at Alum Bay immediately 

 overlying the Barton group were probably of estuary origin. The 

 absence of organic remains leaves a doubt upon the subject. The 

 equivalent bed however at Beacon Cliff on the Hampshire coast, 

 which I shall more particularly describe in a future communi- 

 cation, contains a large quantity of estuary shells mixed with 

 true marine genera, together with the bones of turtles and 

 the teeth of sharks. Guided by these facts, we infer that the 

 white and yellow sands of Headon Hill were the great estuary 

 deposit which introduced the lacustrine conditions under which 

 the lower freshwater group, with the other intercalated estuary 

 beds, w r ere deposited. 



