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Ridge on the west. Tlie latter is really part of the Willunga 

 fault scarp, and its steep western slope is in striking contrast 

 to the topography of the valley under discussion. 



The eastern side of the Bull Creek Range also presents 

 a more broken character, consisting of dissected hill country, 

 dropping rapidly to the Murray Plains. These ridges are 

 clearly remnants of a once extensive peneplain, dislocated by 

 faulting to the west and east. 



They extend northwards beyond the region of the Meadows 

 Valley and form the east and west boundaries of the Onka- 

 paringa Valley in its upper course. There is no sharply-defined 

 watershed between the head of the Meadows Valley and the 

 middle course of the Onkaparinga, and the features are such 

 as to suggest that an ancient north and south valley of mature 

 type and considerable size at one time flowed from the north 

 through the Meadows Valley, and the deposits in its floor 

 and along its sides also* demand such a river. If this be so, 

 where was the southern outlet, and when and under what con- 

 dition was the present system developed ? The upper course 

 of the Onkaparinga has every feature of an ancient mature 

 valley, and is so regarded by Prof. Walter Howchin. 



To the north of Mount Bold it begins to turn more 

 westerly and soon leaves the line of the old valley, which con- 

 tinues southerly. The western ridge is breached to the north 

 of Mount Bold, and through it the Onkaparinga escapes as 

 a deep, steep-sided valley of young character, which it main- 

 tains almost to its mouth. 



Prof. Walter Howchin considers it, in part, an antecedent 

 stream whose lower course during the period prior to the 

 Mount Lofty uplift was. an ever-changing one over a wide 

 fluviatile plain. The extensive deposits of alluvium, gravel, and 

 waterworn boulders of the Kangarilla flats and McLaren Vale 

 represent, in his opinion, a more southerly course of the river. 

 At the time of the uplift its position on the flood plain had 

 migrated to that it now occupies, and hence it becv^me incised 

 in a rising segment of the highlands. 



The drift deposits of the Meadows Valley, though now 

 1,000 to 1,200 ft. above those of the Willunga Plain, strongly 

 suggest a dislocated section of that ancient flood plain. 



At that period the ancestor of the present Onkaparinga 

 had a more continued north and south direction. The Meadows 

 Valley would thus represent a dismembered section of that 

 drainage system which, eventually, became choked to the brim 

 with fluviatile material. The ever-shifting course of the old 

 Onkaparinga tending to a more westerly direction may have 

 been assisted by early warping preceding the later block 

 faulting. 



