274 REPORT ON THE STATE CABINET. 



Plate iv present other phases of two species. It will be observed that 

 in some of these there is a central linear space marked by the bases of 

 cellules, while others present a simple dark line to which the cell-parti- 

 tions are joined. The graptolites of this type, having the character of 

 four simple graptolitic stipes joined at the back, will present in sections 

 a cruciform figure like fig. 5 of Plate iv. When these bodies were thrown 

 down upon the muddy sea bottom, they would become imbedded mainly 

 in two positions. The most common position appears to be that in which 

 the parts retain a vertical and horizontal position, as in the accompanying 

 YiG.i. fig- 4- The lower division, or d, would thus become 



first imbedded ; while the parts b and c would be in 

 the plane of deposition', and a would be the last 

 imbedded. This slaty laminae will separate along the 

 line b, c, either above or below the graptolite, leaving 

 on one side the substance of the cellules and on the 

 other the impression. If the separation take place 

 above, then the bases of the cellules often remain: these are directed 

 obliquely downward towards the base of the stipe, as shown in figs. 2 

 and 7 of Plate iv. If the separation takes place below the substance of 

 the graptolite, in the plane b, c, the cellules of the division d are seen 

 directed upwards towards the apex of the stipe, like fig. 15 of Plate xvi, 

 Canadian Decade. 



The other direction of imbedding would be where the specimens were 

 so deposited that the divisions rested obliquely to the plane of stratifica- 

 tion upon the points c, J, as in fig. 5. In this position, they would, from 

 the accumulating sediment, become compressed as in fig. 6, pj,, 5 



until the parts b, d, and a, c, would approach each other, or 

 come in contact. Lying thus, the slaty laminae separating 

 above or below them, they would present the aspects of 

 figs. 4 and 6, Plate iv; giving no evidence of cellules 

 except at the margins ; unless where the stipe may be fractured when 

 we have an exhibition of a section of the cellules as in fig. 1 of Plate iv. 

 Fig. 6. When the separation takes place in such a manner 



that the parts b a are removed, the parts d c remain, 

 showing the bases of two rows of cellules, as in fig. 

 3 of Plate iv. The various phases presented in large collections of speci- 

 mens of these forms are all explicable upon this view of their mode of 

 growth and manner of imbedding in the soft mud of the sea bottom. 



