284 Geological Society. 



a well-marked and constant feature in the counties of Hertford, 

 Bedford, Buckingham, and Oxford. In the original description of 

 the Melbourn Kock it was confounded with the " Zone of Belem- 

 nitella plena in a remanie condition," as described by Dr. Barrois; but 

 it was now pointed out that the latter horizon is distinct from and un- 

 derlies the latter. Although the zone of Belemnitella plena has been 

 very largely removed by erosion in the district described, there is, 

 nevertheless, evidence that this erosion has gone on to a different 

 extent in each of the localities which have been particularly studied ; 

 and in some places some of the lower portions of the rocks of that 

 horizon seem to have escaped denudation. 



The microscopical characters of the several varieties of rock form- 

 ing the Lower and Middle Chalk of the district were described, and it 

 was shown that the beds containing nodules of a different variety of 

 chalk which occur below the Melbourn Bock, may have been 

 formed by the washing away of the finer particles from a disinte- 

 grating mass of chalk. This mottled chalk and the overlying 

 Melbourn Bock are very similar to the bed found on the same 

 horizon in the Bichmond well. Somewhat similar beds occur, 

 however, at other horizons in the Chalk over the district described 

 in this paper. 



3. " On the Beds between the Upper and Lower Chalk of Dover, 

 and their comparison with the Middle Chalk of Cambridgeshire." 

 By W. Hill, Esq., F.G.S. 



In introducing the subject of this paper, the author referred to the 

 divisions of the tipper Cretaceous series given in the ' Geology of the 

 Neighbourhood of Cambridge' by Messrs. Penning and Jukes- 

 Browne. The Middle Chalk was there described as separated from 

 the Lower by the Melbourn Bock, which also appeared to coincide 

 with a marked palaeontological break, and from the Upper Chalk by 

 the well-known Chalk Bock, this rocky bed, 10 feet in thickness, 

 being included in the Middle Chalk. The division thus made corre- 

 sponded exactly with the Turonian of French authors. 



The author, giving a description of the Middle Chalk seen in the 

 cliffs east and west of Dover, stated that the grit bed of Mr. Price, 

 though much thicker, had all the appearance and structure of the 

 Melbourn Bock, and this, with less hard, but still nodular, chalk above, 

 appeared to be the equivalent of the zone of H. Cuvieri in Cambridge- 

 shire. The zone of Terebratulina gracilis is well marked in the 

 Dover cliffs, and is equal in thickness to that zone as described in 

 the Cambr. Mem., viz. 150 feet. Above this zone the chalk became 

 harder, withered, with lumpy projections, and finally passed into a 

 series of rocky layers, separated by courses of softer chalk, containing, 

 however, hard crystalline lumps. The passage to this rocky chalk 

 was marked by the occurrence of Holaster planus (zone of H. planus). 

 The rocky layers, extending upward for 80 feet, were marked by the 

 presence of numbers of Micrasters, " Chalk with many Micrasters " of 

 the author. His division included all the nodular chalk of Dover, 

 the "chalk with many organic remains" of W. Phillips, and in it were 

 found the fossils recorded as peculiar to Chalk Bock in the Geol. of 

 Cambridgeshire. It appeared divisible into two zones ; the lower, 

 15 feet, with Mieraster breviporus (zone of M. breviporus) ^ may be 



