6 The Eocene Formation of Headon and Alum Bay. 



bank of fossil oyster shells ; the greater part of them are locked 

 into each other in the way they usually live, and many of them 

 have their valves united, clearly showing that they are in the 

 position in which they originally lived and have not suffered 

 removal. A corresponding marine series is also found over the 

 gypsum clays in the Paris basin ; and a bed of bivalves in parti- 

 cular is mentioned as existing, in which the shells are all locked 

 together as in that at Colwell. 



IV. 1 have yet to speak of the upper freshwater, or upper 

 Headon beds. A thin bed of sand of about six inches in thickness 

 covers the upper marine formation, upon which rests a calcareous 

 stratum 55 feet in thickness, every part of which contains fresh- 

 water shells in great abundance. Some of it is composed of a 

 yellowish-white marl. In this, and disposed without any regularity, 

 are hard masses of rock, extremely durable and used for building 

 purposes. Many of the shells embedded in this formation are 

 quite entire ; others again are mere fragments. They consist, 

 like the lower Freshwater, in several kinds of lymnei, helices, and 

 planorbes, and from their perfect state of preservation seem to 

 have lived where they now are. 



In fact there must have once been a vast fi'eshwater lake here. 

 Nor can we refrain from astonishment when we consider how 

 vastly the surface of the earth must have changed since this epoch. 

 What was then the bosom of an extensive lake is now the summit 

 of a hill, while the deep channel of the Solent occupies the 

 position where once must have been the elevations essential to the 

 confinement of a vast body of freshwater. 



Over this is a stratum of clay, 11 feet in thickness, full of 

 fragments of bivalves. This is succeeded again by a bed of yellow 

 clay, upon which lies a bed of friable calcareous sandstone, both 

 without shells. To this succeeds another calcareous stratum con- 

 taining a few shells. In all these last strata ai*e found veins of 

 crystalized carbonate of lime. 



In this formation too, there is found a small globular canellated 

 body, about the size of a mustard seed. It seems to have been 

 rather a poser to the early geologists, so they called it Lymneus 

 fabulus ; Lamarck afterwards gave it the name of Gyrogonites 

 when it was found in the French strata; eventually however it 

 was decided to be the seed of a chara. It abounds, I am told, in 

 the freshwater stone at Gurnet Point a few miles West of Cowes, 

 but I was unable to find one in Alum Bay. 



One of the most interesting results of an examination of these 

 strata is the glimpse it affords us of a series of epochs between 

 the deposition of the chalk strata and the formation of the present 

 surface of the land. The origin of the chalk itself still remains an 



