544 Saunders — Geology of South Beds. 



occasional fragments of rolled chalk, indicating that it has been 

 formed principally from the disintegration of the Kimmeridge bed. 

 It furnished several fossils identical with those observed in this form- 

 ation at Ampthill, at which place also selenite crystals form a con- 

 siderable portion of the mass of the upper beds. This bed of dark 

 clay is succeeded by others of a lighter colour, containing a greater 

 proportion of rolled Chalk and flints, until at the south-east side of 

 the hill — or that facing the Chalk escarpment — the beds are com- 

 posed almost entirely of sand and water- worn fragments from the 

 Upper Cretaceous beds. 



The cuttings between Luton and New Mill End, running parallel 

 with Luton Hoo Park, exhibit some fine specimens of " Chalk-rock " 

 which are interesting, as few continuous sections of this remarkable 

 formation are visible. The first cutting, about a mile from Luton, 

 is entirely in '' Chalk- with-flints," which is here very massive. In 

 the second cutting we have the first occurrence of the " Chalk-rock," 

 where are exhibited in descending order : — 



Chalk-with-flints, 10 feet to 15 feet. 



Chalk-rock, about 2 feet. 



Lower Chalk, without flints, 10 feet to 15 feet. 



So excessively hard is this "rock " that it stands out in striking 

 prominence on the sides of the excavation, it having been im- 

 practicable to level it to the same plane as the softer strata above 

 and below. It does not occur in unbroken continuity, but is con- 

 siderably dislocated at several places, and sometimes, for a few 

 yards, two beds lie parallel to each other at a distance of several 

 feet. 



Contrary to the general character of this bed in other localities — 

 as observed by Mr. Whitaker and others — it is here very rich in 

 fossils ; but, the matrix being so excessively hard, they are with 

 great difficulty extracted. It has a metallic ring when struck with 

 a hammer ; it abounds in green-coated nodules, and is not uniformly 

 compact, but in places can be very easily pulverized. Perforations 

 are occasionally to be seen passing almost through its entire thickness, 

 which have been subsequently filled with dark -brown clay. The 

 Brachiopods, Echinoderms, etc., are always in good preservation, 

 but the more delicate shells of the univalves have perished, leaving 

 casts of their external ornamentation, and a spiral mould of their 

 interior. The Ammonitidce and Nautili have also experienced a 

 similar decay, and, when broken, show the internal divisions of 

 their septa. From my experience in this district I consider that the 

 fossils from this bed have a greater resemblance to those of the 

 Lower Chalk, than to the Upper, or Chalk-with-flints. The following 

 are the principal genera obtained from the section : — 



Terebraiula. 



Ventriculites. 



Cidaris. 



Cephalites, 



Cyphosoma 



Parasmilia 



Serpula. 



Holaster. 



Spondylus. 



Rhynconella. 



Pleurotmaria, 



Turbo. 



A.mmonites. 

 Nautilus. 

 Lamna. 

 Ftychodus. 



Of some of these genera there are several species which await the 

 skill of the Palaeontoloscist to determine. 



