■484 [Dec. 18, 



species of shells, imbedded in silt, the bivalves having their two 

 valves united, and lying evidently on the spot where the inhabit- 

 ants of the shells lived. Both of these modes of association may 

 occasionally be seen in the same pit ; and they are very different 

 from the arrangement of the shelly remains in the till and in the 

 stratified drift. The greatest height from the surface of the chalk 

 at which I have met with these shells, is less than ten feet. 



The rest of the deposit consists of alternating beds and bands of 

 gravel and laminated clay, which, in their upper part, where the ' 

 stratification is less regular than in the lower, are occasionally 

 associated with unstratified masses of yellow loam. The beds, 

 particularly in their lower part, are often obliquely laminated ; 

 and in a cutting of the Yarmouth Railway, between Thorpe and 

 Crostwick, the shelly beds of the crag, which are there seen in 

 contact with a mass of unstratified blue till, exhibit contortions 

 like those which occur in the Cromer Cliffs. 



The epoch of the Norwich Crag was of considerable duration. 

 On the coast of Norfolk, at Mundesley, we see the lowest member 

 of that formation, the pan, overlaid by a fluviatile deposit ; and at ; 

 Euncton Gap * a similar fluviatile deposit is overlaid by a bed con- ( 

 taining shells of the same species that belong to the pan of Mun- ' 

 desley and Happisburgh. 



At Happisburgh the pan is overlaid by a bed of large fossil 

 trees ; and these are buried beneath stratified and unstratified drift. 

 Near Norwich there is no trace of the intervening period when 

 the crag became dry land. Moreover, the only instance I have 

 seen of blue till in that neighbourhood, is in the cutting of the 

 Yarmouth Eailway above noticed ; and in the general absence of 

 this unstratified detritus, there is nothing in the district to define 

 the limits between the crag and the stratified drift, which might 

 pass together for one continuous deposit. 



I will now proceed to describe, in the first instance, the appear- 

 ances I observed in two pits worked in the solid undisturbed chalk, 

 situate within five miles of Norwich. In these pits, twice or thrice 

 a week for several months, I made measurements, and drawings of 

 the surface of the chalk and of the cavities in it, as, during the 

 progress of the works, they became cleared of the overlying 

 deposits. 



In describing these and the other pits referred to in the present 

 paper, I shall adopt the following local terms, used by the work- 

 men. Cavities in the chall?, of greater breadth than depth, they 

 call " drops " ; deep conical or cylindrical pipes in the chalk, they 

 call " pots " ; the overlying gravel, sand, &c. they call " uncallow." 



* The bed of shells at Runcton occurred to the east of the Gap ; but on a 

 visit I made to the spot in the spring of 1845, a fall of the cliff had covered up 

 the bed. To the west of the Gap, however, I found a bed of marine shells, 

 lying, like that to the east of it, above the freshwater deposit. The frozen state 

 of the cliff prevented my obtaining specimens. The shells I found to the east 

 of the Gap were, Natica helieoides, Mya (a large species), Fusus striatus 9 The 

 shells I observed to the west of the Gap were all of the same species, viz. a 

 large truncated gaping bivalve, and had both valves united. 



