ON THE FOSSILIFEROUS TRAKSITION BED IX XORTIIAMPTONSniRE. 345 



Anotber point these Ammonites sLow, at least so it seems to me, is 

 that our Upper Lias species of Dactylloceras are migrants. Several of 

 these species occurring at the bottom of the Upper Lias are so changed 

 from what I imagine to be their parent forms — Grenouillouxi and Pettos, 

 d'Orb. — that T think such changes must have commenced at least before 

 they came to us. 



For fossils to which the nnpibers refer see list. 



1. Transition-bed form between Conamunis and Annulatus. 



2. Transition-bed form differs somewhat from that found in higher 

 beds. 



3. Between Cra^sus and Desplacei. 



•i. Dactylioceras between Crassus and Grenouillouxi. 



5. Hildoceras n. sp. (?), a form more or less of a passage between 

 Levisoni and Serpentinum ; some of the specimens may be H. Frautzi, 

 Reynes. 



6. The specimens of Harpoceras Strangwaysi are very variable in 

 ribbing, some very coarsely ribbed, others very finely ribbed. It is a 

 matter of opinion whether they should be all classed under one name ; 

 at any rate, there is no other name for them. 



7. Mostly young forms, narrow centred, otherwise very like H. 

 simile. 



8. Harpoceras elegans, Sow., non Wright. Some forms between 

 exaratum and elegans. 



9. Vary between simile and lythense, wider centred than true lythense. 

 Ribs not as coarse as in Blake's figure. 



10. Very much like Dumortier's figure of A. lympharum, but the ribs 

 appear a little less sigmoid. 



Summary of Observations. 



M. The Marhtoue Iioclc Bed. — This is the most important bed of the 

 Middle Lias in Northamptonshire, and throughout the country from an 

 economical point of view. Its usual character in the ai'ea referred to in 

 this report is that of a hard, calcareous, and ferruginous rock, varying in 

 colour from a bliiish-greeu, or grey, to a reddish-brown, according to the 

 amount of weathering it has experienced. Where it comes near the 

 surface, as at Arbury and Catesby, it is somewhat fissile, and so of little 

 value except for road mending. Where dug from a considerable depth 

 it may be obtained in large blocks suitable for building purposes, par- 

 ticularly if care be exercised in placing it in the building as it exists in 

 .the bed. 



In no portion of the area investigated is it rich enough in iron to be 

 used as an ore, though in the south-western portion of the county, at 

 King's Sutton, it has been so used. The calcareous matter in it is con- 

 sidered an advantage, as the stone will flux itself. 



Between Catesby and Chipping Warden the bed gets very sandy, and 

 this character is particularly noticeable near to Byfield. 



The thickness varies from 4 feet to 12 feet, the average being about 

 5 or 6 feet. 



The dominant fossils are brachiopods. 



lihijnchoneUa tetrahedra occurs in masses, and Terehratulci punctata 



