MR. A. STR.iHA.N- OX THE LIXCOLNSHTRE CARSTONE. 487 



unconformity, however, has not been confirmed by an examination 

 of the numerous sections of the junction that are exposed. The 

 overlap of the Carstone by the Eed Chalk, which at first sight 

 seems strongly to support Prof. Judd's view of their relations, 

 appears to be due to the steady attenuation of the Carstone 

 northwards that is shared by all the Secondary rocks of Lincolnshire. 

 On the other hand, the Carstone is found not only to rest upon 

 different members of the Tealby Beds in different parts of Lincoln- 

 shire, but to present a strong contrast to all these beds, both in 

 lithological character and in being altogether unfossiliferous, 

 except for the derived fauna, hereafter described. It is, moreover, 

 largely composed of materials, such as flakes and grains of iron -oxide 

 and phosphatic nodules, which there is good reason to believe were 

 derived from the Tealby Beds, and therefore indicate that these 

 latter had suffered considerable erosion before the deposition of the 

 Carstone. 



In general the Carstone is a coarse, reddish-brown, ferruginous 

 grit, made up of small quartz grains or pebbles, small well- 

 rolled phosphatic pebbles, and flakes or spherical grains of iron- 

 oxide. In the southern part of Lincolnshire it is thicker than in 

 the north, and the nodules are smaller. Occasionally the almost 

 obliterated form of a bivalve may be detected, but very rarely. In 

 the north the nodules increase in size and abundance as the 

 Carstone thins, and it is not difficult to pick out rolled Ammonites 

 and bivalves. In its upper part the Carstone becomes more clayey, 

 and passes finally into a red clay or marl, in which Belemnites are 

 common, and which forms the base of the Red Chalk. The small 

 particles of quartz, Lydian stone, &c., which make up a large part 

 of the Carstone, range up in gradually decreasing abundance into 

 the lower beds of the Eed Chalk. Two or three lines of concretions 

 (not derived, but formed in place in the Carstone) may be traced 

 for many miles at a scarcely varying distance below the Red Chalk. 

 Eventually the Carstone thins out altogether, and the con- 

 glomeratic character then invades the Red Chalk. The nodules 

 which occur in the Red Chalk are similar to those of the Carstone, 

 where the Red Chalk rests on the Neocomian clays, but north of the 

 Humber, where it overlaps the Oolites, are made up fragments of 

 those rocks. The Carstone of South Lincolnshire would thus 

 appear to be the expansion of a " coprolite-bed," and in its 

 behaviour may be compared to the Chloritic Marl and the Cambridge 

 coprolite-bed, or to what takes place on a great scale at the base of 

 the Carboniferous rocks, where the limestone becomes conglomeratic 

 when the red basement-beds are absent. 



The outcrop of the Neocomian rocks and their thicknesses in 

 different parts of Lincolnshire are illustrated in the accompanying 

 figures (facing p. 492). The series thins out northwards through 

 the steady attenuation of each member, rather than by a marked 

 unconformity of the beds above, as is seen in the following table of 

 thicknesses : — 



2l2 



