IS^ Saunders — Geology of South Bedfordshire. 



resemblance to the Gault, but is most probably a member of the marl.^ 

 So far as observed there appears but little difference in the fossil 

 remains of these strata, the chief distinction being the much greater 

 abundance of Ammonites varians in the Lower Chalk than in the 

 other beds.'' One peculiarity respecting the Cephalopods is the total 

 destruction of the shell itself, its place being occupied by a brown 

 ochreous substance, and in most instances, when a specimen is frac- 

 tured, the internal divisions of the chambers are most beautifully 

 indicated by the same substance. Only one specimen has been dis- 

 covered with any trace of the shell ; this was in the fragment of the 

 outer whorl of a large individual, which, when entire, must have 

 measured sixteen inches in diameter, in this case the outer shell was 

 absent, but the internal separations were preserved. The Ammonites 

 varians varies in size from an inch to upwards of a foot in diameter, 

 and the same remark will apply to a species of Nautilus occurring 

 in the same locality. The shells of Ostrea, Terehratula, Pecten, 

 etc., have not suffered the decay incident to the Ammonites and their 

 congeners. Most of the Cephalopods are very much compressed and 

 contorted, more particularly the Ammonites varians, which some- 

 times present such anomalous forms as to render it scarcely 

 recognisable. The fossils obtained from this cutting are mentioned 

 in the subjoined list. 



At Leagrave is an excavation in the Drift formation, that exhibits 

 a series of alternating sands, gravels with sub-angular flints, and 

 clays, containing rolled fragments of fossils from the Secondary 

 strata. At the south-eastern termination of the cutting a member of 

 the Lower Chalk appears, that has been coloured a light yellow by 

 the percolation of water through the superincumbent bed of clay. 



About midway between Leagrave and Luton is another bed of the 

 Lower Chalk. This is hard and compact, with almost a metallic 

 ring when struck with the hammer, and so indurated, that blasting 

 has been necessary in working it. The natural cleavages have a 

 greenish tinge. This bed has, numerically, a great many fossils, 

 but the species are few, the most prevalent forms being Terehratula 

 and Inocerami. At Luton the Lower Chalk is softer than the pre- 

 ceding, and runs along the valley of the Lea as far south as Wheat- 

 hamstead. 



Between Luton and New Mill End is a series of cuttings in the 

 Upper White Chalk. This contains an abundance of flints, in layers 

 at irregular intervals, and also several thin seams of a grey clay, 

 somewhat resembling fuller's earth. These clay bands may be 

 seen at Harpenden, where the roads have been altered for the con- 

 venience of the new railway. The fossils from these cuttings are those 

 characteristic of the Chalk-with-flints, of which a list is subjoined. 

 From Harpenden to St. Alban's the Upper Chalk is exposed, capped 

 with drift sands and gravels, and as we approach the latter town 



1 When the Lower Chalk is full of water it presents the appearance described 

 here by the author, of a " bed of dark clay ; " the Lower Chalk is always rich in iron 

 pyrites. — Edit. 



^ A, varians is remarkably abundant in the Totternhoe stone of this part. — Edit. 



