296 Transactions. — Geology. 



endeavoured to show this in Plate XX., fig. 1, representative 

 of Cormack's siding ; fig. 2, of H. i\llen's. (The sub-volcanic 

 deposit at Bain's is very similar to these.) In these it will be 

 noticed that the diatoms, Polycystince, and sponge-spicules are 

 nauch smaller than in figs. 4 and 5, which represent the forms 

 found in the supra-volcanic calcareous diatom earth in Jack- 

 son's and Bain's ; also that in the former or sub-volcanic de- 

 posits Stcplianopyxis abounds, and is absent, or, at any rate, 

 rare, in the latter. Fig. 3 shows a peculiar deposit on the 

 Totara Estate. It is a continuation of the upper layer of 

 Bain's sub-volcanic layers, and lies somewhat higher. I am 

 unable to account for the minute character of the diatoma- 

 ceous remains found here unless it be a question of gravity, 

 and that the diatom mud was shaken up and the heavier 

 forms fell to the lower depths. 



Although the large forms are much more abundant in 

 Jackson's and Bain's, and much more perfect, it must not be 

 assumed that they are absent in the other deposits, for they 

 are found, but only in fragments and scarce. Mr. Grove ac- 

 counts for their better preservation in Jackson's by the larger 

 forms of the sponge-remains and the great quantity of the 

 spongioliths : the diatom-valves falling amongst them would 

 be protected. 



I suggested previously that the hard white material was 

 altered and semi-fused diatom earth — altered by the action of 

 the intense heat of the volcanic lava in the dyke. This theory 

 seems confirmed by the conditions of the layers at Bain's and 

 at Allen's. Here the volcanic remains consist of tufi", or 

 volcanic ash, and this seems to me to have settled down on 

 the diatomaceous ooze in a cooled state, for I find that the 

 white earth immediately attached to the tuff is just as rich in 

 diatoms as any other part of the deposit ; and, indeed, some 

 of the tulT is perforated by or surrounds hollows filled up by 

 pure diatom ooze. 



I have not yet referred to the Ototara limestone lying 

 above the diatom earth and the volcanic remains, and feel very 

 diffident in putting forth any theory on the geological con- 

 ditions and ages of the deposits, but I will do so in order to 

 invite discussion and obtain information from those well calcu- 

 lated to give it. 



It seems to me that at a very early period of the history of 

 this part of the world matters were very quiet, and that there 

 was a greater excess of vegetable life, and that animal life was 

 then less abundant. This period of rest was disturbed by vol- 

 canic irruptions, and possibly the levels were altered. After this 

 disturbed era had passed away a fresh growth of vegetable and 

 animal life followed, but, owing to some change of conditions, 

 the animal life, as represented by the Polycystince and sponges. 



