236 M. HAWKINS JOHNSON, F.G.S., 



fluid. I did so, and immediately saw that I had got a beautiful 

 and delicate structure of a most definite character, in the case of 

 the Septaria from the London Clay having the appearance repre- 

 sented in this drawing (Fig. 3). 



Being satisfied of the existence of this structure, my next 

 difficulty was to preserve it so as to be able to show it to others at 

 any time, and what with air bubbles, disengagement of gas, 

 shrinkages and leakages, &c., I had so much trouble that I 

 should be ashamed to lay the details of my failures before the Club, 

 although they might possibly be edifying. I found at last the 

 best plan to be to wash carefully, by a gentle stream of water, 

 until all trace of acid was removed, then very gradually to heat 

 the water to boiling, so as to get rid of all air, and to mount in a 

 cell with freshly boiled distilled water. It is necessary to stop the 

 action of the acid while there is still a portion of the solid stone 

 left, as this latter makes a firm foundation for the delicate tissue 

 exposed, which, while it maintains its connection with the part 

 still imbedded, retains its original form unaltered. 



The structure thus exhibited has the appearance of a soft mass 

 permeated in every part by anastomosing canals. It is evidently 

 of an organic nature, and suggests very forcibly that great division 

 of the Protozoa, the sponges. The Septaria, from the Kimmeridge 

 Clay, have a very similar structure ; the Clay Ironstone nodules 

 also, which are probably of the same nature as the Septaria, except 

 that the calcium has been partly replaced by iron, present the 

 same appearance ; so also do the Phosphatic Nodules of the Cam- 

 bridge deposit, and those from the Gault in other places. The 

 structures of these several bodies do not appear to be absolutely 

 identical, but may be said to have a generic resemblance. Of 

 course there are considerable differences of colour. 



Having established to my satisfaction the organic character of 

 all these bodies, I was tolerably prepared to see, without surprise, 

 anything whatever ; I was, nevertheless, almost startled when I 

 found that the well-known nodules of Iron Pyrites, so common in 

 the Chalk, and often known as thunderbolts, are not only of 

 organic origin, but that the organic structure is still present in 

 these masses, merely waiting to be uncovered — such is un- 

 doubtedly the case. Slices of these nodules ground smooth, and 

 then subjected to the action of strong nitric acid, show this struc- 

 ture in relief on the surface, the bi sulphide of iron by which it 



