104 POTERIOCRIND^ EXTRACRINUS. 



several feet long, whose loicer surface only presents the arms and fingers of these fossil 

 animals, expanded like plants in a Hortvis Siccus; whilst the upper surface exhibits only 

 a congeries of stems in contact with the under surface of the lignite. Tlie greater 

 number of these stems are usually parallel to one another, as ii' drifted in the same 

 direction by the current in which they last floated. 



The mode in which these animal remains are thus collected immediately beneath 

 the lignite, and never on its upper surface seems to shew that the creatures had attached 

 themselves, in large groups, (like modern barnacles), to the masses of floating wood, 

 which, together with them, where suddenly buried in the mud, wliose accumulation 

 gave origin to the marl, wherein this curious compound stratum of animal and 

 vegetable remains is Imbedded. Fragments of petrified wood occur also in the lias, 

 having large groups of mytili, in the position that is usually assumed by recent mytili, 

 attached to floating wood." — Brklgeivater Treatise, vol. 1, page 4.37. 



As the waters of the sea during the deposition of a considerable portion of the lias, 

 were subject to frequent irruptions of mud which rendered them turbid, and the sea 

 bottom incoherent marl, conditions not generally favourable to the Pinnastella, as 

 from the soft nature of much of the sedimentary matter the bottom was not sufficiently 

 firm for their permanent attachment, the valuable suggestions of Dr. Buckland 

 become of considerable importance as affording a probable solution of the most 

 frequent mode of existence of the Extracrinus Briareus. 



The fossil Crinoids imbedded in the lias are frequently covered with a delicate film of 

 iron pyrites, which gives them the appearance of bronze figures. This metalliferous 

 coating has been apparently deposited by a natural process of electrotyping, originating 

 in the currents of terrestrial magnetism which traverse the earth's crust. 



It has been computed that a single specimen of Extracrinus Briareus contained 

 in its indurated skeleton no less than one hundred and fifty thousand ossicula, each 

 of which is equivalent to a little bone. Our own calculation extends the number 

 much beyond that previously made by Dr. Buckland in his Bridgewater Treatise; and 

 Dr. Mantel!, in the " Wonders of Geology," as the following details will shew. 



Omitting the plates which cover the dome-like integument over the abdominal 

 pouch, and which are very numerous as may be seen on reference to PI .12, fig. 1, b, 

 as also the minute plates which studded the integuments over the sulci along the 

 rays, as well as taking a lower estimate than even the facts warranted of the number 

 of joints both in the rays, and side arms, and likewise making the column shorter 

 than it really must have been in the mature animal, the total number of ossicula or 

 calcareous joints composing the skeleton or indurated frame work cannot be less 

 than seven hundred and forty one thousand, seven hundred and ten ; and as each 



