Speight and Wild. — Weka Pass Stone and Amuri Limestone. 89 



another rock of different lithological composition is in proportion as these 

 rocks form part of the earth's crust in the locality where the limestones are 

 being laid down. The criteria of unconformity in general, apart from the 

 possibility of chemical erosion on the plane of contact, will be the same as 

 between limestone and another rock. In Kindle's paper attention is drawn 

 to the difference in dip of the two limestones in question, and to the 

 decided surfaces of erosion of the lower limestone. The photographs that 

 he uses to illustrate his paper are quite convincing, and show pronounced 

 differences in the contact as compared with that between the Weka Pass 

 and Amuri limestones, and we have seen no locality where similar pictures 

 could be obtained from the contact of the two New Zealand rocks. 



For the reasons given above the authors consider that the contact 

 between the two limestones is not due to erosion, and that after the deposit 

 of the lower bed no emergence from the sea took place before the second 

 limestone was deposited. Some alteration in depth or in the conditions 

 of deposition no doubt occurred, but they were of no greater amount than 

 that which takes place when a bed of different lithological character is laid 

 down in a perfectly conformable sequence. 



It has been pointed out that both above and below the nodular layer 

 there is an interstratification of greensand in the limestone, the deposition 

 being conformable, which shows that slight oscillations of level or conditions 

 took place. The phosphatic nodules are exactly analogous to those forming 

 now on ocean-bottoms at depths of over 100 fathoms in association with 

 greensand, and such do not form on a shore-line. Such nodules are fre- 

 quently found in the Cretaceous limestones of Europe and America without 

 an unconformity being demanded, although some lapse of time and change 

 of conditions must have occurred. The phosphate nodules occurring in the 

 Cretaceous beds of the south of England and the north of France and in 

 Belgium usually lie at the base of the series which succeeds another after 

 some lapse of time. In some cases, however, distinct unconformity has 

 been demonstrated on account of the presence of pebbles and rolled fossils, 

 the break being of more decided character and amounting to an uncon- 

 formity, but in other cases there is no pronounced break. 



The association of these nodules with a bored surface seems to indicate 

 clearly that the boring took place not on a shore-line, but on a sea-bottom 

 formed of a soft calcareous ooze before it had consolidated and hardened 

 into rock. The borings extend to such a depth beneath the surface that it 

 may be doubted whether it is possible for marine organisms to tunnel such 

 a distance into hard rock, whereas if it be admitted that the boring took 

 place before the rock had consolidated and while it was actually in process 

 of deposition there is no difficulty. The filling of these deep tunnels with 

 greensand, as has been pointed out, certainly suggests boring on a sea- 

 bottom. Although many marine organisms have the power of making 

 burrows, it occurred to us that they were in all probability made by marine 

 worms, and therefore we applied to Dr. Benham for his opinion on the matter. 

 In a private letter he says, " Unfortunately we know nothing, so far as I 

 can find out from monographs on the Polychaeta, &c, about the burrows 

 in deep water. When the dredge is used the surface of the mud, &c, will 

 still be disturbed ; and even if the worms are captured the walls of the bur- 

 rows, if any, will fall in, and the burrow, of course, will be smashed. So that 

 I find no reference at all to burrows of worms living beyond the littoral- 

 zone area. But we may expect that if they are formed at these greater 

 depths they, too, will be U-shaped. You ask at what depths worms live 



