362 Capt. Cullen's Notice of the Geological Features 



ceptidn of the first five or six miles, is through an open level 

 country, of perhaps fifteen miles square, as if it had been formed 

 by the abstraction of a part of the central chain of hills which 

 divide the southern and northern portions of this tract into 

 two narrow valleys. The Saghilair river is crossed nearly in the 

 centre of this open space ; and it is immediately on reaching 

 its northern bank that the quartz is observed to assume quite 

 a new character, to constitute, as appears subsequently, one 

 of the most important features in the remainder of the route. 



A green schistus seems to prevail throughout this plain, and 

 it continues as far north as Iddamacul, as may be observed 

 from an examination of the wells ; latterly also appearing above 

 the surface in ridges of considerable elevation. 



The strata of schistus in the bed of the Saghilair, which are 

 nearly vertical, and of a bright green colour, present a very 

 interesting appearance. 



The direction of the strata at the ford corresponds with that 

 of the bed of the river ; and the stream, which appears subject 

 to a very rapid rise and fall, has in consequence worn nu- 

 merous deep narrow channels through the slate, presenting 

 on all sides sharp perpendicular dykes of fifteen or twenty feet 

 high, while they are often but a few inches in thickness. Al- 

 most immediately on reaching the north bank of the Saghilair, 

 the quartz, which hitherto had never been met with but in 

 the seams of the slate, and there seldom exceeding a breadth 

 of eighteen inches, is now observed alone in immense blocks, 

 and continuous masses, of fifty or sixty feet wide. Their di- 

 rection corresponded, I think, generally with that of the strata 

 of schistus, but they appeared above the soil unaccompanied 

 by any other rock, and forming ridges of such magnitude 

 and extent, as to give them the appearance of the summits 

 of quartz hills, commencing to be denuded of soil, and forcibly 

 impressing one with the idea of being in the vicinity of gra- 

 nite: nor was the impression, perhaps, altogether without 

 foundation, as the small fort of Iddamacul, twenty miles further 

 north, is built on an insulated hill of sienite. 



The quartz ridges became gradually more numerous and 

 extensive on my progress up the valley ; but I lost them after 

 leaving Iddamacul, and striking off to the westward by Gid- 

 deloor towards the Nulla Mulla range. Nothing could pos- 

 sibly be more interesting or striking than this small pile of 

 sienitic masses, which, possessing all the peculiar rugged out- 

 line of a granitic hill, afforded the most singular contrast to 

 the smooth, bare, undulated contour of the clay-slate ranges 

 on either side of the valley. The valley was here seven or 

 eight miles wide, and this hill rose out alone, as if forced up 



from 



