4 PRELIMIXARY OBSERVATIONS. 



The numbei' and arrangement of the plates surroimding the body, differing so essentially 

 from those of every other genera, preclude the idea that any transformation ever took 

 place. 



As the chief end and aim of science is truth, we trust we shall stand excused for thus 

 adverting to the errors so prevalent with regard to the Crinoidea, and which it is neces- 

 sary to notice in order to arrive at a right miderstanding of the subject. 



Professor Owen, in the Edinburgh New Philosophical Journal, No. 6-5, July, 1842, 

 in allusion to the probable solution of some interesting phenomena respecting various 

 extmct species of animals, suggests the possibUity that the atmosphere of our planet has 

 undergone a material chemical change, — namely, from a dense fluid which contained 

 much carbon, and but a small portion of oxygen as compared mth the more in^-igorat- 

 ing and lighter medium which at jn-esent siuTounds the earth. 



Such a physical state of things would not only satisfactorily accoimt for the gradual 

 introduction of animals and plants approaching to the existmg Fauna and Flora, but 

 would explain some other physiological questions of great interest. 



When investigating the lower fossiliferous rocks, we have fi-equently speculated on 

 the probable physical conditions of the medium wliich enveloped our planet at the 

 period of their deposition. If we adopt Professor Owen's ingenious and highly probable 

 suggestion, and suppose the atmosphere, by its excess of carbon, to have been a dense 

 heavy fluid, whose specific gravity was only a few degrees lighter than water, we have a 

 clear exposition of the adaptation of the structiu'e of molluscous animals, and the Ocean 

 Lilies at remote geological epochs, to the peculiar physical conditions of an atmosphere 

 whose force operated on the surface of the globe with a degree of energy much beyond 

 the atmospheric pressure at the present time. 



The Encrinites, which were spread over the bed of the ancient seas, were so completely 

 protected by calcareous plates, that but a small portion of thefr softer substance was left 

 exposed to a pressure which it may be conjectiu'ed it was unfitted to resist, and thefr 

 forms were in every respect well calculated to meet the supposed atmospheric influence 

 as exerted on the medium in which they Uved. 



The shells wliich inhabited the waters dm-ing the earlier ages of oiu- planet, also 

 indicate a physical adaptation to such a state of things as that limted at by Mr. Owen, 

 for they were either of a highly arched form, or else were fm-nished with internal spfres, 

 both modes of structure being well adapted to resist the crushing effects of an atmo- 

 sphere, the pressiu'e of which must have operated with considerable mtensity at the 

 lowest depths of the ocean ; and wluch might well be supposed capable of injiuing the 

 fragile material which enveloped the mollusca, unless coimteracted by some such wise 

 provision as that which forces itself on our attention. 



