208 SUBAPENNINE STKATA [Ch. XIII. 



Three divisions of the Antwerp Crag have been recognized by the 

 Belgian geologists : first, the Uppermost or Yellow Crag, in which 81 

 species of shells were known when I gave a list of them in 1852 ; sec- 

 ondly, the Middle Crag, from which 94 species were known ; and 

 thirdly, the lowest or Black Crag, from which 65 shells had been ob- 

 tained. This bed derives its name from the dark color of most of the 

 sand, which consists of green grains of glanconite. 



There can be no doubt that the two first formations are referable to 

 the Older Pliocene period, the Yellow Crag containing about 60 per 

 cent, of recent species, while the Middle or Grey Crag contains about 

 50 per cent. Their close connection with the Eed and Coralline Crag 

 of Suffolk is equally clear, for in a list of 52 shells from the Upper or 

 Yellow Crag, and of 94 from the Middle Crag, there are only 7 species 

 which are not found in the British formations of corresponding age. 

 'As we might have expected, the Upper Antwerp Crag agrees more 

 with the Red Crag of England, while the shells of the Middle Ant- 

 werp Crag correspond more with the Older or Coralline group of 

 Suffolk. 



But when we come to the Lowest or Black Crag we are beginning 

 to pass beyond the limits of the Older Pliocene formations, and ap- 

 proaching the Miocene. Only two-thirds of the shells agree with those 

 of the Coralline Crag, and somewhat less than half of the fossil species 

 are identifiable with species still living. They seem to form the first 

 links of a chain of passage by which we shall in time be conducted 

 without a break to those older formations, the Upper Miocene of Bel- 

 gium, to be treated of in the next chapter. 



Normandy. — I observed in 1840 a small patch of shells correspond- 

 ing to those of the Suffolk Crag, near Yalognes, in Normandy ; and 

 there is a deposit containing similar fossils at St. George Bohon, and 

 several places a few leagues to the south of Carentan, in Normandy; 

 but they have never been traced farther southward. 



OLDER PLIOCENE FORMATIONS IN ITALY. 



Subapennine Strata. — The Apennines, it is well known, are com- 

 posed chiefly of secondary rocks, forming a chain which branches off 

 from the Ligurian Alps and passes down the middle of the Italian pen- 

 insula. At the foot of these mountains, on the side both of the Adri- 

 atic and the Mediterranean, are found a series of tertiary strata, which 

 form, for the most part, a line of low hills occupying the space be- 

 tween the older chain and the sea. Brocchi, as we have seen (p. 183), 

 was the first Italian geologist who described this newer group in detail, 

 giving it the name of the Subapennine ; and he classed all the tertiary 

 strata of Italy, from Piedmont to Calabria, as parts of the same sys- 

 tem. Certain mineral characters, he observed, were common to the 

 whole ; for the strata consists generally of light brown or blue marl, 

 covered by yellow calcareous sand and gravel. There are also, ho 



