400 Transactions. 



of Recent species, these figures are quoted to show the great palaeonto- 

 logical difference between the lowest and the highest beds. So great is this 

 difference that it is natural to look for breaks in the stratigraphical sequence, 

 and the temptation is naturally great to lay emphasis on any slight local 

 irregularity in the stratigraphy and to magnify it into an unconformity. 

 A consideration of this difference perhaps causes one to demand from an 

 observer who holds to the idea of a conformable sequence a special explana- 

 tion of the rapid faunal change, since the whole series as developed in North 

 Canterbury is not more than 3,000 ft. thick. 



(b.) Explanation of Rapid Change of Life- forms. 

 We believe that this explanation is to be found in these three considera- 

 tions : (1) A possible isolation of New Zealand during the late Mesozoic ; 

 (2) a possible lingering of archaic types ; (3) the very slow rate at which 

 the deposits accumulated. 



(1.) Isolation. 



Evidence as to the previous isolation of the eastern coast-line of New 

 Zealand is somewhat conjectural. It is, however, certain that in the 

 middle Mesozoic great rock-movements were in progress, and the early 

 Mesozoic rocks of New Zealand were folded and elevated into mountain- 

 ranges of great size. So important was this movement in New Zealand that 

 it is reasonable to inquire whether it extended beyond the boundaries of 

 the present land. It is then fomid that to the north the rocks of New Cale- 

 donia of early Mesozoic age are also folded. In the south the quartz gravels 

 of the lowest members of the series of younger rocks in Campbell Island 

 were evidently derived from folded and metamorphic rocks similar to those 

 of Otago. There is no definite evidence of further extension, for the Beacon 

 sandstone of South Victoria Land can hardly be cited in this connection. 

 If the New Zealand shore-lhie at that time (the close of the Mesozoic) ex- 

 tended from very low to high latitudes a measure of isolation would be thus 

 obtained. It is noteworthy that iii the folded and highly eroded rocks 

 of early and middle Mesozoic age marine reptiles were numerous. Trigonia, 

 Inoceramus, and Belemniles were well represented ; so that in regard to these 

 organisms at least there is a suggestion that during the great interval 

 throughout which immense rock foldings and erosion were in progress the 

 fauna of the coast-line suffered but little from the competition of new and 

 more vigorous organisms. 



(2.) An Archaic Fauva. 

 It is well known that at the present day many forms long extinct in 

 Europe and America linger and maintain an existence in the south-west 

 Pacific. The Trigonia of Australia, (Jeratodus, Sphenodon, and such genera 

 as Strutkiolaria are, of course, examples, and it is possible that owing to 

 causes apart from isolation many Mesozoic forms had survived in New 

 Zealand after they had become extinct elsewhere. 



(3.) Slow Bate of Deposition. 

 (i.) Conglomerates. — We are inclmed to ascribe much of the advance 

 in the fauna to the mere lapse of time. It is true that the total thickness 

 of the strata is not more than 3,000-3,500 ft. at Waipara, where all the 

 strata are present ; but it is also known that nearly every member of the 

 series has a thicker development elsewhere — to take a single example, the 

 bottom hundred feet of sands and gravels is represented by 7,000 ft. of 



