1858.] WETHERELL NODTJLES IN CRAG. 31 



axis of a Graphularia Wetherellii. Very fortunately, not only the 

 quadrangular form of the fossil is preserved, but also the radiated 

 structure, as seen in the section. 



Now this discovery in itself is not important, but it becomes 

 interesting when the same thiQg is proved to occur in nodules found 

 in the Crag. On the table are some oviform nodules from the Crag, 

 which exhibit the same kind of nucleus. In many instances 

 the subcylindrical form of the nodule somewhat corresponds with 

 that of the contained fossil ; but the oviform nodules just mentioned 

 show that this is not always the case. 



Examining many of the nodules, we shall find ^ broken Nodule 



that, in the first place, as a general rule, there is -^^^^ t"'^ .f^^' ."-' 

 ., Vy 7 7' n j_ ^ -i • j_i vmq for tts axis a 



the Graphularia, or a fragment oi it, in the cen- ^o?5/wi of the stem 



tre. Sometimes, however, the coral is entirely of a G-raphularia. 

 wanting, there being only a quadrangular, a sub- 

 angular, or a cylindrical tube, corresponding to /^^^s. 

 the different portions of the stem that has been Z \ \ 

 removed. Kext there is a generally subcylindri- fif/ ^I^^S 

 cal or fusiform coating of clay over the fossil, f'''/^mSBl 

 varying in diameter in different specimens from /))""^S|^^^i 

 half-an-inch to an inch. Upon this first coating u ^HR' t^| 

 is placed a series of indurated layers of clay, || ^P^^'^ 

 often blackened by iron, varying in number to \\ .■ 

 ten or more ; and lastly there is another argilla- '% li / 

 ceous coating, finishing off the nodule into an \s\ ;; / 

 oval and sometimes a pyriform shape, with a ^^^^L,^^^^ 

 rough external surface. 



Now this fiirst coating of clay is generally of a fusiform shape 

 and in juxtaposition to the nucleus. It is not usually so compact 

 as the layers which enclose it; and sometimes it is so soft and 

 powdery, that it may easily be scraped away with a penknife. It is 

 more or less ferruginous ; and instances are not wanting where it has 

 almost entirely crumbled away, leaving a hollow tube, almost large 

 enough to admit of the introduction of the little finger. 



The layers vary in thickness in different specimens; sometimes 

 they are not thicker than tissue-paper, and at others about half an 

 inch in thickness. Again, these layers are often striated longitu- 

 dinally — the strias being very numerous and thick-set, and 

 occasionally having waved lines passing transversely over them; 

 and well-preserved nodules exhibit their ■striae on aU the layers. 

 Some instances occur where the layers are lent inwards. The 

 longitudinal striae are in a few instances broader, more prominent, 

 and less numerous. The material of the nodules investing the coral 

 appears to be entirely argillaceous, with different modifications, and 

 with a variable admixture of iron*. 



I will now briefly call attention to some other nodules of a 

 different character. In them the centre is composed of a sub- 

 cylindrical mass of minute bodies of a very peculiar character. 



* The first and second coatings of clay effervesce with acid in a greater degi'ee 

 than the other layers. 



