110 PRINCIPLES OF CLASSIFICATION. [On. X 



Paris, because the greater number of the fossil shells were specifically 

 identical. For the same reason rocks found on the Gironde, in the South 

 of France, and at certain points in the North of Italy, were suspected to 

 be of contemporaneous origin. 



A variety of deposits were afterwards found in other parts of Europe, 

 all reposing immediately on rocks as old or older than the chalk, 

 and which exhibited certain general characters of resemblance in their 

 organic remains to those previously observed near Paris and London. 

 An attempt was therefore made at first to refer the whole to one pe- 

 riod ; and when at length this seemed impracticable, it was contended 

 that as in the Parisian series there were many subordinate formations 

 of considerable thickness which must have accumulated one after the 

 other, during a great lapse of time, so the various patches of tertiary 

 strata scattered over Europe might correspond in age, some of them 

 to the older, and others to the newer, subdivisions of the Parisian 

 series. 



This error, though almost unavoidable on the part of those who 

 made the first generalizations in this branch of Geology, retarded se- 

 riously for some years the progress of classification. A more scrupu- 

 lous attention to specific distinctions, aided by a careful regard to the 

 relative position of the strata contaiuing them, led at length to the con- 

 viction that there were formations both marine and freshwater of various 

 ages, and all newer than the strata of the neighborhood of Paris and 

 London. 



One of the first steps in this chronological reform was made in 1811, 

 by an English naturalist, Mr. Parkinson, who pointed out the fact that 

 certain shelly strata, provincially termed " Crag" in Suffolk, lie decidedly 

 over a deposit which was the continuation of the blue clay of London. 

 At the same time he remarked that the fossil testacea in these newer 

 beds were distinct from those of the blue clay, and that while some ot 

 them were of unknown species, others were identical with species now 

 inhabiting the British seas. 



Another important discovery was soon afterwards made by Brocchi in 

 Italy, who investigated the argillaceous and sandy deposits replete with 

 shells which form a low range of hills, flauking the Apennines on both 

 sides, from the plains of the Po to Calabria. These lower hills were 

 called by him the Subapennines, and were formed of strata chiefly marine, 

 and newer than those of Paris and London. 



Another tertiary group occurring in the neighborhood of Bourdeaux 

 and Dax, in the south of France, was examined by M. de Basterot in 

 1825, who described and figured several hundred species of shells, which 

 differed for the most part both from the Parisian series and those of the 

 Subapennine hills. It was soon, therefore, suspected that this fauna 

 might belong to a period intermediate between that of the Parisian and 

 Subapennine strata, and it was not long before the evidence of super- 

 position was brought to bear in support of this opinion ; for other strata, 

 contemporaneous with those of Bourdeaux, were observed in one district 



