C'h. XIII.] OF TERTIARY FORMATIONS. 1§3 



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 containing 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, flanking 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 

 (the Valley of the Loire), to overlie the Parisian formation, and in an- 

 other (in Piedmont) to underlie the Subapennine beds. The first exam- 

 ple of these was pointed out in 1829 by M. Desnoyers, who ascertained 

 that the sand and marl of marine origin called Faluns, near Tours, in 

 the "basin of the Loire, full of sea-shells and corals, rested upon a lacus- 

 trine formation, which constitutes the uppermost subdivision of the 

 Parisian group, extending continuously throughout a great table-land 

 intervening between the basin of the Seine and that of the Loire. The 

 other example occurs in Italy, where strata, containing many fossils sim- 

 ilar to those of Bourdeaux, were observed by Bonelli and others in the 

 environs of Turin, subjacent to strata belonging to the Subapennine 

 group of Brocchi. 



Without pretending to give a complete sketch of the progress of dis- 

 covery, I may refer to the facts above enumerated, as illustrating the 

 course usually pursued by geologists when they attempt to found new 

 chronological divisions. The method bears some analogy to that pur- 



