Mr. Lyell on the relative ages of Crag, 407 



The strata dip 15+° to the S.S.W. 



Mr, Atkinson is of opinion that the impressions are principally- 

 due to worm -tracks. 



A paper was afterwards read, " On the relative ages of the ter- 

 tiary deposits commonly called Crag, in Norfolk and Suffolk," by 

 Charles Lyell, Esq., V.P.G.S. 



This paper contains the results of Mr. Lyell's examination of the 

 crag, with reference to the three following points : — First, The 

 direct superposition of the red to the coralUne crag, as originally 

 pointed out by Mr. Charlesworth in 1835 : Secondly, Whether the 

 remains of mammalia are really imbedded in regular and undis- 

 turbed marine strata in the Norwich crag : Thirdly, Whether the 

 proportion of recent shells, as compared to the extinct, is decidedly 

 larger in the crag of Norwich, so as to indicate a posteriority in age 

 relatively to the Suffolk crag. 



1. Of the superposition of the red on the coralline crag, the 

 author found distinct proofs in the sections at Ramsholt and Tat- 

 tingstone, as previously indicated by Mr. Charlesworth, and in 

 quarries near Sudburne pointed out to him by Mr. Bunbury. At 

 Tattingstone the coralline crag consists chiefly of greenish marl, 

 with discontinuous layers of stone, and the number of corals is 

 very small ; but both at that locality and Ramsholt, the red crag 

 rests on denuded beds of the coralline. At Sutton, near Wood- 

 bridge, Mr. Lyell was enabled to ascertain, by the assistance of 

 Mr. W. Colchester, that the red crag in some places abuts against 

 a vertical face of the coralline, as well as overlies it; and that 

 in consequence of the irregularities in the outline of the face, the 

 two deposits have a deceptive appearance of alternating. He also 

 ascertained, in addition to the above evidence, that the older or 

 lower strata must have acquired a certain consistency before the 

 newer were accumulated, because the calcareous sand or comminuted 

 shells and zoophytes, of which the former are composed, is perfo- 

 rated to the depth of 6 or 8 feet from the surface by the tortuous 

 borings of pholades, the shells of which are frequently found at the 

 bottom of the tubes, the remainder of the perforations being filled 

 with the sand of the superjacent red crag. The most northern 

 point to which the coralline crag has been traced, is Sizewell Gap, 

 several miles north of Thorpe. 



2. With respect to remains of mammalia being imbedded in 

 undisturbed marine beds in the Norwich crag, Mr. Lyell stated, 

 that an examination of this crag in the neighbourhood of Southwold 

 and Norwich had convinced him, that instead of the deposit being 

 purely marine, it is fluvio-marine, containing every where an inter- 

 mixture of land, freshwater, and sea-shells, with the bones of 

 mammalia and fishes. The formation is exposed along the coast, 

 at Thorpe, near Aldborough, where it may be seen at low-walser 

 resting on the coralline crag ; but it is most largely developed in the 

 neighbourhood of Southwold, where the author examined it accom- 

 panied by Capt. Alexander. In that district, it varies greatly ia 

 character, consisting of irregular beds of sand, shingle, loam, and 



