FIRST EXPEDITION 479 



:entres of eruption, are frequently scoriaceous in a marked degree, 

 forming spongy masses, light and porous as pumice-stone. In 

 a few places, the basalt of the coulees is columnar, as at the waterfalls 

 in the Endeavour, between Williams' station and Branigan's. 

 jThe basalt is of the usual character, but contains occasional horn- 

 blende crystals, and much olivine. It also contains lievrite (silicate 

 of iron) in geodes. 



GATES' LOOKOUT is a volcanic centre of a different character 

 ithe deep-seated stump or " NECK" OF A CRATER, which once discharged 

 .showers of ashes from its mouth. It forms a conspicuous mountain 

 of tuff, and can be seen from Isabella Creek to cut through the 

 escarpment of a thick bed of white sandstone. This rock is an 

 agglomerate of volcanic debris, with a certain rude bedding 

 icourses of larger alternating with courses of smaller bombs having 

 a dip to the east at about 15 degrees. That the bombs are 

 mot detached fragments of an already consolidated rock, but have 

 (been consolidated from a molten mass while whirling through 

 the air, is proved by the spherical envelope of vesicular basalt which 

 invariably enfolds them. The interior of the bombs is a mass of 

 iblack and green crystals of augite (?) and olivine. They range from 

 ian eighth of an inch to a foot in diameter. 1 



After skirting the east side of the MORGAN TABLELAND (a 

 [denuded fragment of the horizontal sandstone) for a distance 

 (of about 4 miles, we ascended a "bald" (i.e., treeless) mamelon 

 inear its northern extremity. This mamelon is another of the 

 [volcanic foci. A larger one a low hill, partly scrubby and partly 

 jbald rose from the flats about 2 miles to the east. From its 

 base extensive volumes of smoke marked the whereabouts of a num- 

 :ber of intending selectors who had left Mr. Starcke's camp in the 

 morning, and were now burning the grass. 



We next passed north-westward by the end of the sandstone 

 cliffs of the Morgan Tableland, over slate ridges (below the level 

 of the base of the sandstone) strewn with fragments of white quartz. 

 In about 2 miles to the north we crossed from the left to the 

 right bank of a stream running south, and about 3 yards wide, 

 which must be a feeder, if not the main head, of the MORGAN. 

 It was fringed by a belt of scrub, through which we had to cut a 

 passage with tomahawks. We followed up the right bank of this 

 creek to the north for rather more than 2 miles, crossing a 

 tributary coming from the hills to the west. At the end of the 

 2 miles the creek was found to trend to the west, the valley 

 presenting a steep wall of sandstone which forbade the further 

 passage of horses in that direction. We therefore crossed to the left 

 bank in the hope of finding a passable gap through the sandstone 

 range further to the north. After skirting the range to the 



i For further details, see Geol. Map attached to Report by A. Gibb Maitland, on the 

 Geology of the Cooktown District. Brisbane, by Authority, 1891. R. L. J. 



