THROUGH THE LOWER AND UPPER STRATA. 29 



OBSERVATIONS. 



The author has attempted, in this chapter, to give a succinct ac- 

 count of the geological distribution of fossil organic remains, belong- 

 ing to the animal and vegetable kingdoms. This, he conceives, will 

 interest the learner, for whose use it was chiefly intended, more than 

 a detailed enumeration of the genera or species supposed to be pecu- 

 liar to different rock formations. With respect to fossil conchology, 

 he is inclined to believe, that the attempt to identify the strata of dis- 

 tant countries by the isolated occurrence of any particular species of 

 shell, has been carried farther than a sound induction from facts or 

 analogy would warrant. His opinion on this subject, given in the 

 second edition of this work, he will here insert : — "It may be doubt- 

 ed, whether the occurrence of similar organic remains is sufficient to 

 identify strata in distant parts of the globe ; for, could we admit that 

 strata are universal formations, and extended from the frozen to the 

 torrid zone, it seems more than probable, that the animals which liv- 

 ed on any one particular stratum, would be of very different species 

 in different latitudes." — We know so little respecting the forms or 

 habits of the animals classed by the conchologist, that we are far from 

 being certain whether many shells which he regards as belonging to 

 different species, or even genera, are not mere varieties of form, oc- 

 casioned by difference of age or situation. Such a change is ascer- 

 tained to take place by age, in shells of the genus Cyprcda. 



In animals like the mollusca, which have no internal skeleton to 

 determine their form, the construction of the external shell may, prob- 

 ably, admit of considerable variation under a change of circumstances. 

 Few conchologists, excepting M. D^Avilla, have made accurate ob- 

 servations on the living animals inhabiting oceanic shells. His inter- 

 esting work, entitled '•'•VHistoire Naturelle eclaircie dans une de 

 ses parties princi'pales, la Conciiologie ; et augmentee de la Zoomor- 

 phase, ou Representation des Animaux d coquilles, avec leurs Expli- 

 cations,''^ — presents us with some truly extraordinary forms of mol- 

 luscous animals, of which we could not have had a remote notion from 

 the mere study of the shell. 



In strata belonging to one formation, and in adjacent districts, the 

 existence of certain shells, whether we regard them as distinct species 

 or as varieties, may be of use, in identifying any particular bed : — and 

 in distant countries, where we find the same remarkable species of 

 shell associated with any other remarkable species in considerable 

 numbers, it may serve to identify a particular rock formation, where 

 the mineral character of the rock may be very different from that in 

 which the observer has been accustomed to meet with them. The oc- 

 currence of a considerable number of Gryphaeae, the GrypTicEa arcuata, 

 in a bed of blue clay in the mountains round the Lake of Annecy, in 

 Savoy, served the author as a key to discover to what formation the 

 calcareous strata belonged, when their mineral characters would have 

 indicated a more ancient series. 



Vegetable organic remains have not, till recently, been studied with 

 the attention which they deserve and require. — These remains are 

 never found entire, as i& frequently the case with th® skeletons and 



