1850.] MANTELL ON THE GEOLOGY OF NEW ZEALAND. 



325 



others spherical ; many were entire, whilst others were broken, and 

 glittering with yellow and brown crystals of calcareous spar, with 

 which all the interstices of the septaria were lined or filled. Some 

 of these masses were hollowed out by the action of the waves into 

 regular basins, which at low-tide stand up from the sands full of 

 water, and are three or four feet deep, forming excellent foot-baths 

 for the weary pedestrian. 



" Many of these septaria struck me as curious from the zone or belt 

 of cone-in-cone clay with which they were encircled, as in the sub- 

 joined sketch (fig. 6), which represents the usual form and appear- 

 ance of one of these zoned nodules. 



Fig. 6. — Septarium with a zone of Cone-in-cone Clay, 



Fig. 7. — Section of a Septarium, from Onekakara, 



a, a. Spherical body of the 



Septarium. 



b. Fragment of bone imbed- 



ded in the Septarium. 



" Fig. 7 is a section of the same, exhibiting the cone-like structure. 

 The direction of the apices of the cones is towards the centre of the 

 nodule ; the coating of the other part of the sphere (fig. 6, a, a) is 

 composed of clay with crystals of selenite ; the cones are represented 

 disproportionately large, to render the structure intelligible. These 

 septaria, with the exception of the belt of cone-in-cone clay, are so 

 like those I recollect seeing extracted from the London clay off the 

 coast of Sussex, and used for Roman cement, that I think they may 

 be applicable to the same economical purpose. I gave some to Capt. 

 CoUinson, R.E., who had it burnt and ground by a mason, who pro- 

 nounced it worthless ; but I still put faith in my cement, and not 

 in the lime-burner*. 



* A portion of one of these nodules has, through the kindness of Sir Henry De 

 la Beche, been analysed at the laboratory of the Museum of Practical Geology ; 



