Geological Society of London. 137 



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 Rock, may have been 

 formed b} r the washing away of the finer particles from a disinte- 

 grating mass of chalk. This mottled chalk and the overlying 

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

 horizon in the Richmond 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.GS. 



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

 divisions of the Upper 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 Rock, which also appeared to coincide 

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

 the well-known Chalk Rock, this rocl<y 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 Rock, 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 Terehratulina 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, weathered, 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 Holasler 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 Rock in the Geol. of 

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

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

 considered by some to be an extension of the zone of H. planus, the 

 form which marks the passage from the soft to the hard chalk. In 

 the remainder M. cor-testudinarium was common (zone of M. cor- 

 testudinarium) . 



Seen in thin sections under the microscope, the structure of the 



