THE EUROPEAN SEAS. 



225 



great amount of change in latitude is necessary 

 before a complete change is brought about in the 

 species inhabiting deep-sea zones; the interval be- 

 tween the Arctic circle and the Tropic of Cancer 

 does effect it. Kesidual deep-sea forms of tropical 

 assemblages cannot, therefore, be expected beneath 

 such as belong to the higher sea-zones of more 

 northern assemblages. The foregoing considerations 

 may be of use to the palaeontologist and geologist, 

 and will frequently be referred to in the sequel. 



Isolated groups of fossil remains are not uncom- 

 mon amidst our old sedimentary beds ; a remark- 

 able instance has been noticed by M. Barrande. In 

 one of the " lower divisions " of the great palaeo- 

 zoic series of Bohemia, he has described the occur- 

 rence of a patch of as many as sixty species, which 

 forms do not agree with those characterizing the 

 " lower division." These forms have lived in the 

 beds in which their remains are found ; they ulti- 

 mately cease, and have been surmounted by beds 

 which contain the forms of the "lower division." 

 These sixty species are isolated, but they appear 

 again as a component part of the fauna of the 

 " upper division " of the same palaeozoic series. 



To these isolated assemblages of upper palaeozoic 

 amidst lower palaeozoic forms, M. Barrande has 

 given the name of "colonies." They are true 

 " outliers," and will serve to suggest curious and in- 

 teresting geological inferences in the earlier history 

 (both natural and physical) of the European area. 



Q 



