204 On the Orthoceratites of Scotland. [March, 



pipe filled with the matter of the surrounding rocks. This is the 

 case with all the perfect multilocular testacea which I have had an 

 opportunity of examining in a petrified stale. The pipe, having an 

 external opening, must have been filled at the period of the depo- 

 shion of the rocks. The shell and the partitions, on the other 

 hand, have been altered, and their particles have assumed a new 

 and more crystalline arrangement, intimating a previous state of 

 fluidity. The cavities of the chambers, having no external open- 

 ing, are filled with various crystallized substances, which must 

 have entered in a state of solution through the pores of the shell or 

 the partitions. 



When the shell is destroyed, or the partitions broken, then the 

 chambers are found filled with the matter of the surrounding rock. 

 The cavities of the chambers of the 0. sulcata and 0. vndata are 

 filled with clay-iron-stone. One specimen of the 0. cyl'mdracea is 

 imiK'dded in a septariuvi, the base of the shell reaching to the 

 centre of the mass, and the apex projecting beyond its circum- 

 ference. That part of the shell situated in the external covering, 

 and extending to about five-eighths of an inch, is perfectly regular 

 and entire ; but near the base of the shell, and towards the centre 

 of the septarium, the partitions of the chambers are broken, and 

 the cavities filled with clay-iron-stone and iron-pyrites.* 



111. — GKOGNOSTIC HISTORY. 



The species of the genus orthocera, which have now been 

 described, were found in the strata of the county of Linlithgow, a 

 district of country entirely composed of rocks belonging to the 

 Independent Coal Formation of Werner : species 5, 6, and /, I 

 obtained from a bed of slate-clay at the Blackburn Colliery, in the 

 parish of Livingstone. This bed alternates with white sand-stone, 

 slate-coal, and compact lime-stone. The slate-clay and the lime- 

 stone contain entrochites, and other spoils of the Ocean ; while the 

 beds of sand-stone and coal contain the remains of vegetables. 

 Such strange arrangements of organic remains are not uncommon 

 in the coal-field of the Lothians. One specimen of species 3, 

 included in the septarium, was found in this bed of slate-day; but 

 other specimens of the same shell, and the remaining species, were 

 found at different places in the middle of the county, imbedded in 

 the strata of lime-stone which traverse the high grounds to the 

 south of Linlithgow, f 



In the whole extent of these strata no remains of the belemnite 

 have yet been observed. Tliese must have existed had the orthoce- 

 rathebeen merely the concamerated alveolus of that curious petri- 



• If this scptariu?!! wns in a state of fusion at iJs formation, in what manner 

 was the shell of (his orlhnceratite preseivod from incorporating witli the melted 

 mass, and enabled to retain lis position ? 



t The characters of this liinc-str.ne are taken notice of in my acconnt of the 

 Old Silver Mine in Linlithgowshire, inserted in the jtnnali of PhitosopZ-y, 

 p. 119 of tliis vol. 



