152 Rev. Mr Wheweirs Address to the Geological Society, 



great interest, since it involves the question of the value and 

 right mode of application of the test of the relative number of 

 recent species, on which Mr LyelPs classification, or at least his 

 nomenclature, is founded. I conceive that in a matter of ar- 

 rangement any arbitrary numerical character must lead to vio- 

 lations of Nature's classifications ; and can only be considered as 

 an artificial method, to be used provisionally till some more 

 genuine principle of order be discovered. 



Mr Clarke, in his survey, has noted as one division of the 

 diluvium of his district, a clay of a yellowish or bluish hue, 

 containing rolled pieces of chalk. This deposit is of great ex- 

 tent and thickness in East Anglia and the neighbouring parts ; 

 and is worth notice, since this deposit is one main cause of the 

 geological confusion and obscurity in which that region is in- 

 volved. In the neighbourhood of Cambridge this diluvial de- 

 posit, is called the brown clay ; and I can state, from my own 

 experience, that the recognition of it as a separate bed at once 

 rendered the stratification clear, where it had long been unin- 

 telligible. 



Before quitting our stratified rocks, I may notice the com- 

 munications respecting some of their fossils which we have re- 

 ceived, particularly that of Mr Williamson on the fossil fishes 

 of the Lancashire coal-field, and the establishment of the new 

 genus Tropaeum, separated from the Hamites of the green sand 

 by Mr Sowerby. 



In attempting to pursue a stratigraphical order, we are com- 

 pelled to reserve for a separate head the notice of unstratified 

 rocks, since their age and history are only known by the mode 

 in which they interrupt and disturb the rest of the series. We 

 have not had many communications respecting European, 

 rocks of this character ; but we cannot but be struck by the 

 subversion of ancient ideas which results from the investigations 

 of Messrs Murchison and Sedgwick. They have shewn that 

 the granite of Dartmoor, and consequently that of Cornwall, 

 formerly considered as one of the earliest monuments of the pri- 

 meval ages of the earth's history, is posterior to the deposit of 

 the culm measures. 



Advancing to newer phenomena, we find the evidences of 

 change still unexhausted. We cannot but reflect how familiar 



