Speight. — The Tertiary Beds of the Trelissick Basin. 



327 



of the Porter coming in from the west and junctioning with the main 

 stream close to the road-crossing. This tributary rises in Mount Enys and 





43 Zb 



^^^:^s:imm^m^^ 



W.N.W. 



E.S.6, 



Fig. 3. — Section along Whitewater Creek, Distance. 2 J miles. Direction. W.N.W.- 

 E.S.E. 1. greywacke ; 2a, sands, greensands : 'lb. marls, &c. ; 3, tutr 

 beds ; 4. limestone ; 5, sands, sandy clays, shales, and conglomerates— 

 Pareora beds. 



Mount Olympus, peaks of the Craigieburn Range, and flows in a south- 

 easterly direction across the whole series. The section exposed below the 

 limestone is as follows (see fig. 3) : — 

 Limestone. 



Volcanic tuff, of uncertain thickness but probably over 1,000 ft. 

 Calcareous greensand, more calcareous in its lower portions — in fact, 

 it is in its lower portions an argillaceous limestone, flaky and 

 hard, and showing some resemblance to the lower bed of lime- 

 stone ; indeed, it is extremely probable that it actually represents 

 that bed in this section. It is 12 ft. thick, strikes north-east, 

 and has a dip to the north-west of 45°. 

 Volcanic tuff, containing numerous fragments of rock, and glauconitic 

 in character owing to decomposition, and passing down into a 

 true tuft', the total thickness being 60 ft. 

 Marl, fine-grained and flaky at times, containing a proportion of 

 sandy materia], sometimes decidedly sandy. The dip is here 

 steeper, reaching 65°, and the thickness of the bed 500 ft. 

 Greensands and sands, the latter sometimes concretionary, with thin 

 beds of coal in their lower levels, striking N. 80° E., and dipping 

 in a northerly direction at an angle of 45°, the total thickness 

 being 950 ft. Although there is thus a variation in dip between 

 this and the overlying marl, there is no evidence of a break. 

 These beds rest unconformably on greywacke exposed in the 

 channel of the creek. 

 The series here enumerated is somewhat different from that recorded 

 by Hutton, the discrepancy arising, no doubt, through the obscuring of 

 parts of the section by covering gravels, different observers having an 

 opportunity of examining only portions of the sequence. I can see, how- 

 ever, no sign of an unconformity, any variations of the dip and strike being 

 what might be expected from the circumstances of the deformation of the 

 beds by folding. It is natural under those circumstances that both will 

 slightly vary from place to place. 



In Coleridge Creek, the westerly extension of Porter River, the volcanic- 

 tuff beds become more important. The following sequence occurs in the 

 lower part of the creek : — ■ 

 Limestone. 

 Marl and ash beds interstratified, the former being both grey and 



white, and the latter in places calcareous and with fossils. 

 White sands, interstratified with volcanic beds, the sands passing 

 down into greensands. 



