2 FAUNA OF THE CORNBRASH. 



Dr. A. Oppel, in 1856-8, subdivided the " Juraformation " into zones, but his 

 observations on the Cornbrash were not very numerous, and he observed it only in 

 Wiltshire, where it and the underlying strata are very similar and with difficulty 

 distinguished except by the fauna. Thus he made the following statement : 

 " The Forest Marble and the Cornbrash I join in one zone and name them after 

 one of the most important fossils — the beds of Terebratula lagenalis." 1 But neither 

 Davidson in the study (a) nor H. B. Woodward in the field knows of any example 

 of Waldheimia (" Terebratula ") lagenalis in the Forest Marble (j3). It may be 

 taken therefore as unknown at that horizon. On the other hand, Oppel, finding 

 no Ammonites macrocephalus at Stanton, Wilts, concluded that there were none 

 anywhere in the Cornbrash (p. 456), and assigned the beds in which they were 

 already known to occur in Yorkshire to the Kelloway Rock (p. 509). These 

 misunderstandings have long since been rectified in this country, but, through the 

 influence of Oppel and our own classification according to lithology rather than 

 to paleeontology, the English Cornbrash has long been supposed on the Continent 

 to occupy a position below the zone of Ammonites macrocephalus ; or rather, the 

 strata below that zone have been identified with the Cornbrash of England. 2 



As it happens, the zone of Macvocephalites macrocephalus, as it is now called, 

 is a very important one, and occupies a peculiar situation in the series of Jurassic 

 rocks. As Neumayr explained some twenty years ago in a paper on " Die 

 Greographische Verbreitung der Juraformation," 3 the whole series may be divided 

 according to their geographic distribution into two parts — the Lower and the 

 Upper. The map which illustrates that paper shows the rocks which are referred 

 to the Lower Jurassic from the Lias to the Bathonian inclusive, as occurring only 

 in parts of Europe, the North of Africa, and the Caucasus range ; but those 

 referred to the Upper Jurassic from the Callovian to the Tithonic, as transgressing 

 beyond these limits to Russia, eastwards to Cutch, the Salt Range, the Himalayahs, 

 and northwards to Siberia. This is a result, confirmed as it is by deposits still 

 further removed in the Arctic regions, in Western Australia, and in South 

 America, of world-wide significance. In both these cases the lower strata of 

 the subdivision are the most widely distributed. Each series commences with a 

 maximum and is gradually reduced to a minimum. The Upper Jurassic Series 

 commences with the Macrocephalites beds represented by its various forms, as in 

 Russia, 4 Cutch, 5 Franz Joseph Land, 6 and Bolivia, 7 etc. 



1 ' Juraformation,' p. 453. (a) ' British Fossil Brachiopoda,' vol. i, p. 99. (/3) ' Lower Oolitic 

 Bocks of England ' ('Jurassic Bocks of Britain,' vol. iv, p. 579). 



2 Eenevier, " Chronographie Geologique," 1897. 



3 'Denk. Math. Nat. Class. K. Acad. Wiss. Wien/vol. 1, 1885. 

 * Nikitin, 'Geol. Karte Buss.,' 1885, pi. 17. 



s Waagen, ' Pal. Ind.' 



6 Newton, " Quart. Journ. Geol. Soc," vol. liii. 



7 Steinmann, " Neues Jahrb.," 1881. 



