426 Transactions. — Geology. 



The two outcrops at the Eed Bluff, C and D, are caused 

 by a fault which has parted the band and displaced one 

 portion horizontally (see section). Beyond outcrop D the 

 band disappears in a little bay, but reappears again a short 

 distance further on at E, where it has been bent into a 

 syncline showing as a fourth outcrop at F. These are the 

 only exposures of the grit in this locality. As in the case of 

 the Takapuna ash-beds, they are fossiliferous throughout. 



That these ash-beds were laid down in water is abund- 

 antly proved by the included fossils (Bryozoa) they contain. 

 The angular character of the whole of the material, both large 

 and small, would point to its being deposited at no great 

 distance from where it originally fell ; whilst the fact that 

 the bands lie conformably between the other members of 

 the Waitemata series tends to indicate that these grits were 

 laid dovvn horizontally and subsequently tilted by the same 

 forces which caused the inclination of the other sedimentary 

 beds. 



As already mentioned, these grits in several places are 

 fossiliferous. Indeed, the fossils are abundant and can be 

 readily seen standing out from the weathered surface. In the 

 softer strata above and below they hardly occur at all, the 

 gritty floor having been evidently more favourable for their 

 growth, and the calcareous nature of the grit having aided in 

 their preservation. Mr. S. H. Cox says that these deposits 

 of grit represent the commencement of the volcanic outbursts 

 which culminated in the formation of the volcanic breccia at 

 the north Manukau Head, and further adds that this vol- 

 canic activity may account for the great absence of life during 

 the latter part of this period. This explanation, however, 

 does not seem satisfactory, since it is in the volcanic beds 

 that fossils are most numerous ; whilst, moreover, many of 

 the Polyzoa and Bryozoa occur in the positions they occu- 

 pied whilst living. 



This brings us to a consideration of how the material 

 reached its present position. It is hardly conceivable that it 

 was ejected into the air and fell as the product of a single 

 shower, for in that case one would expect to find the fossils 

 either at the top or bottom of the beds — possibly in both 

 places — whereas some, at any rate, of the exposures are 

 fossiliferous throughout their entire thickness. The more 

 probable explanation is that the material was furnished 

 gradually, and carried along the bottom by currents working 

 out from the sources of supply. In this way a large amount 

 of volcanic material could be spread over the bottom with 

 sufficient slowness to admit of the growth of marine organ- 

 isms, yet rapidly enough to mark off the deposit from other 

 members of the series. 



