304 Sir H. H. Howorth—North Norfolk Geology— 
and Segerberg so often alluded to above (C), and to the suggestive 
papers by Brogger on the Huloma Niobe fauna,’ and by Rudemann on 
the Dictyonema shales of New York State.” 
In conclusion, therefore, I maintain that within the Cambro- 
Ordovician transition series of Britain and Scandinavia we are able to 
recognize with certainty the following common horizons—(E) zone of 
Lsograptus gibberulus = zone of Didymograptus hirundo; (D) zone of 
Didymograptus balticus = base of zone ot Didymograptus eatensus ; 
(C) base of Ceratopygekalk = Shumardia beds; (B) base of Dietyo- 
graptus shales= zone of Dictyonema sociale; (A) zone of Peltura 
scarabeéoides = zone of Peltura scarabeoides; but that no one of these 
marks any distinctive forward step in the evolution of the trilobites. 
If trilobites must be retained as the basis of systematic classification, 
it becomes necessary to begin the Ordovician system somewhere within 
the Acerocare zone of Sweden and at the base of the Wiobe beds of 
Britain. This, however, I think would be quite unsatisfactory, and 
I would urge that instead we follow the lead of the Scandinavian 
geologists and agree to separate the Cambrian and Ordovician systems 
in such a way that the Dictyonema-bearing beds may be included with 
the rest of the graptolites within the latter. 
Il1.—Norre Norrotx Grotogy: THe CHartk anp its. DIsLocaTIon. 
By Sir Henry H. Howorrn, K.C.I.E., F.R.S., F.G.S. 
(Concluded from the June Number, p. 277.) 6 
condition of the Chalk seems to me quite incomprehensible. -Let 
us analyze the position rather more closely. The champions of ice 
as the cause of the phenomenon we are discussing appeal to it in 
two forms—ice-sheets and icebergs. Mr. Reid was, I-beleve;—the 
originator of the notion that the dislocations of the Norfolk Chalk 
were due to an ice-sheet, which means an ice-sheet occupying the 
North Sea. . 
I should like to quote a sentence or two from the Survey Memoir 
on the country round Cromer in support of this statement. We are 
there told that ‘‘at Trimingham the chalk has been forced by glacial 
action much above its normal height”’ (op. cit., p. 3). Again, speaking 
of the difficulty of ascertaining the entire thickness of the Cretaceous 
rocks at Trimingham, we read, ‘‘ Owing to the disturbance from glacial 
action and other causes no very satisfactory dips can be obtained on 
the coast”’ (op. cit., p. 5). 
On p. 82 of the same memoir Mr. Reid claims that he was the 
first who, in 1880, suggested that the disturbances in question were 
caused by the pressure of the zce-sheet, which, during the greatest 
intensity of the cold, probably filled the bed of the North Sea and 
ploughed up large masses of chalk, driving them laterally into the 
beds (Guotoercan Macazine, 1880, pp. 55-66). This view was still 
1 Nyt Mag fur Naturvidensk. Kristiania, 1896. 
2 New York State Museum, Bull. 69, p. 934, 1908. 
