[Proc. Rot. Sue. Victoria, 28 (N.S.), Part 1.. 1915] 



Akt. IV. — Geological Notes Northern Territory, Australia. 



By K. J. DUNN. 



, (With Plates X. and XL;. 

 [Read June 10th, 1915] . 



Remarkdble Sedimentation. 



The accompanying plate is a faithful representation, natural 

 size, of the surface of a two-inch core obtained in boring for coal 

 in No. 1 Hoie, Borroloola, McArthur River, at a depth of 255 

 feet from the surface, in sedimentary rocks, considered by Dr. 

 Jensen. Government Geologist, as of Carboniferous age, and known 

 as the Bukalara Beds. 



In the plate the white portion represents very fine white siliceous 

 sand, now altered to quartzite; the dark portions represent black 

 to dark grey shales that were originally deposited as mud or silt 

 in thin laminae. In some places extremely thin layers of sand 

 alternate with layers of black shale. 



What renders this core specially remarkable is the complicated 

 nature of the sedimentation and the manner in which it has been 

 modified and interfered with subsequently to deposition, and while 

 yet in a soft condition. The original deposition no doubt was in 

 thin layers more or less horizontally disposed, but this condition 

 was very different to its present confused structure. 



The plate, of course, does not represent a straight vertical section 

 through the bedding, but a circular section through the beds. By 

 joining the edges at a and 1>, the original cylindrical form of the 

 core would be restored. 



Dr. Jensen, to whom 1 am indebted for the specimen from which 

 the photograph was taken for the plate, is of the opinion (Plate 

 III., Bulletin No. 10, Geological Survey, Northern Territory) that 

 worms were the cause of the extraordinary structure seen in the 

 core, and with this view the writer coincides as the only feasible 

 explanation. The worms must have burrowed into ami through the 

 soft, recently deposited layers of sand and silt, with the result 

 that, in places the lamination was disturbed, or interrupted, as at 

 the points marked c, d, e, f. g, on the plate, and at other places. 

 In all cases the burrows were filled in with hue sand, and these sand- 



