356 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 26, 



To these succeed around Paris, whence the first pomts of comparison 

 were obtained, a deposit of a soft hght-coloured calcareous freestone 

 abounding in marine exuviae ; whilst in the vicinity of London we find, 

 in resembling superposition, a thick mass of tough, tenacious, brown 

 and dark grey clays, also with marine remains, but in far less abun- 

 dance, and not so well preserved. Measuring the strata by their rela- 

 tive importance and general bearing, there appears to be an analogy of 

 position and condition. As masses they are equivalent ; but our ques- 

 tion is with time, and that has but a very uncertain relation to masses. 



From the frequent and almost constant variations of thickness 

 which tertiary strata so generally exhibit, and from the compara- 

 tively local and limited expansion of many divisions, we ought to 

 examine carefully the thinner as well as the thicker beds of the 

 singularly-varied series of the Paris tertiaries ; to trace the thinner 

 ones in their greater development, and the thicker ones in their de- 

 creasing importance, and to note the variations and progress of their 

 faunas. In all cases where considerable differences present themselves 

 at distant points in beds of the same presumed age, we may most 

 usually expect to meet at intermediate localities with intermediate 

 characters, providing always that we have reason to suppose any con- 

 nexion of original sea-bottom, such as probably existed at the first 

 tertiary period. Thus the thick argillaceous deposit of London day, 

 at London, on the one hand, and the nearly pure calcareous deposit 

 of Calcaire grossier at Paris, on the other hand, might be expected to 

 show in their range towards each other, provided they were syn- 

 chronous, some indications of a common origin. At the same time, 

 the groups of organic remains should, notwithstanding the difference 

 of chemical and mechanical conditions, exhibit some of the analogies 

 dependent upon like conditions of age and of approximate geogra- 

 phical position. 



Passing over for the present the beds between the chalk and the 

 London clay, we will confine ourselves to the examination of the 

 question of the latter bemg the equivalent of the Calcaire grossier. 

 To understand how it came to be so considered, we must begin wdth 

 the excellent work which first brought the fossils of this period pro- 

 minently under notice. 



Long before any systematic arrangement of the English and French 

 tertiaries was attempted, the abundance and good state of preservation 

 of the fossil shells found in the clay-cliffs of Barton had attracted the 

 attention of Brander, by whom figures and descriptions of them were 

 pubUshed in 1766*. When next, in 1803, Lamarck examined the 

 shells of the Calcaire grossier of Grignon, he met with many which 

 agreed vdth those figured by Brander from Barton, and with these 

 he inferred them to be coevalf. In 1811, Parkinson J examined the 

 fauna of the London clay of London and Sheppey ; and in the same 

 year the cutting of the Highgate tunnel enabled Mr. Sowerby and Mr. 

 Wetherell to add considerably to the list of the London clay fauna. 



A general resemblance of lithological character between the strata 



* Fossilia Hantoniensia. f Annales du Museum, tome i. 



X Trans. Geol. Soc. 1st Ser. vol. i. p. 324. 



