346 EEPORT— 1891. 



more rarely in tlie same manner. Bands composed of ossicles and frag- 

 ments of shells sometimes extend for a considerable distance. The 

 characteristic ammonite, A. spinatus, is exceedingly rare. 



K, L. The Transition Beds. — These beds in Northamptonshire usually 

 consist of a rather thin baud of grey friable marl passing upwards into a, 

 red sandy clay, though the latter is not unfrequently absent where the 

 foi'mer may be distinctly identified. 



The marl, in its most typical form, appears to consist of a highly 

 porous, calcareous matrix containing numerous small rounded grains of 

 the same composition, which latter maj^ be plentiful enough to give it 

 an oolitic character. It weathers reddish-brown on exposure. The 

 lower portion sometimes passes into a hard compact limestone, but even 

 then, apart from the fossils, it can usually be identified, though its exact 

 junction with the rock bed may remain doubtful. 



The thickness, including the red sandy clay, seldom exceeds 6 inches, 

 but at Milton they together measure a foot. 



The red sandy day does not, as a rule, contain fossils, but at Milton 

 it contained a good many casts of belemnites and evidences of other 

 fossils. 



The lower portion of the Transition beds may be described as a highly 

 fossiliferous bed, both as regards individuals and species, though, as the 

 fossils are mostly small, and require a good deal of patient searching for, 

 it would not always give a stranger to it that impression, and of course 

 it is not equally fossiliferous everywhere. 



The most characteristic fossil is Ammonites acuhis, and it is doubtful if 

 this species has been found out of this particular zone, though some of the 

 smaller specimens from beds above may be very close to it. The sudden 

 apjjearance of this ammonite in threat niiinhers, and its equally sudden dis- 

 appearance or change are matters of considerable interest that require 

 further investigation. The other ammonites, of the genus Stephanoceras, 

 are nearly equally abundant, but some of these com.e fully developed, and 

 also occur in higher beds. 



The striking fossils here, however, are the gasteropods, as will be 

 noticed by the list. 



Another noticeable feature of the Transition beds is the generally small 

 size of the fossils (gasteropods excepted), and particularly of the brachio- 

 pods and other survivors of the Middle Lias period. Small specimens of 

 Rhynclionella tetrahedra are probably more abundant than any other 

 fossil. 



G, I. The Fish Bed. — The Fish bed proper is mostly a single band of 

 argillaceous limestone or of flat limestone nodules, both of which split 

 easily in a longitudinal direction after exposure to atmospheric influences 

 for some time, and in doing so nearly always expose a number of fragment- 

 ary fish remains. 



The nodules with us are never concretionary, and in all probability 

 their pai'ticular condition has been brought about by water percolating 

 through joints in the bed, because the upper surface is mostly more 

 convex than the lower, and they all show the same horizontal stratification 

 (compare description of Bugbrook section). 



The stone has characters which enable a geologist to readily identify 

 it when in its normal condition. It is yellowish or quite white on the 

 exterior, and bluish-grey, light-brown, or yellowish inside, according to 

 the amount of weathering undergone. 



