TJ HORN EXPEDITION — GENERAL GEOLOGY. 



Restin£f af^uinst the escarpment on the north side of Crown Point is a well- 

 defined shingle-beach, rising to an elevation of, at least, fifty feet above the Finke 

 Channel ; whilst well-rounded pebbles reach up to the base of the Desert Sandstone 

 on Crown Point, and much gravel is scattered over the low-level country for 

 several miles northward. East* noted that the channel of the Finke at this place is 

 strewn with large boulders of red granite, some weighing about a quarter of a ton. 



It would appear that prior to the formation of Cunningham Gap (the break 

 in the escarpment), the waters of the Finke were impounded to form an extensive 

 lake, during which the shingle collected and reached higher and higher levels as 

 the lake-water gained depth. The I'ock-structure of the gorge, as seen in Crown 

 Point, consists in descending order of Desert Sandstone, about fifty feet, resting 

 nearly liorizoutally on false-bedded, friable, felspathic sandstone and purple, hard, 

 sandy clays. The water-level of the lake reached as high as the base of the 

 Desert Sandstone, and an easy drainage was presented at its junction with the 

 underlying beds, which in themselves especially, also because of the southerly dip, 

 could not offer much resistance to the passage of water. The liberajtion of the 

 impounded water was, in the first instance, brought about in all probability by the 

 undermining of the coping of Desert Sandstone and its final removal. The 

 irruption of the water was at one stage probably sudden, as a rush of detritus was 

 piled up in confusion to form the low cliffs ))ordering tlie Finke at a distance of 

 four miles away. 



Yellow Cliff, at the soutli-east bend of the Finke, near Crown Point Head 

 Station, which is about fifty feet high, consists of : — Yellow and buff sandstone, 

 strongly false-bedded near the top, intersected by vertical joints filled with 

 limonite, enclosing pebbles of Desert Sandstone and quartzite ranging from small 

 gravel to 2|- x ih inches, occasionally two feet cube ; the pebbles are somewhat 

 rounded and smoothed, many of them are standing on edge. At the east end of 

 this blufi" the sandstone is very tumultously-bedded, and in its basal part contains 

 a conglomerate of about four feet thick. 



On the banks of Adminga Creek there is a thickness of thirty feet of con- 

 solidated river-gravel, consisting of alternating bands of coarse and fine material. 

 The pebbles, for the most part, consist of Desert Sandstone, ironstone, and 

 common opal, all of local origin. 



River Terraces.— The best exemplification of this feature is in the valley of 

 Alice Creek near its junction with the River Hugh. Alice Creek is shallow, and 



• (viii.), p. 44. 



