BY H. I. JENSEN. 505 



with horizontal Cretaceous, Jurassic, and Laramie beds will be 

 discussed more closely later. 



The position of the Glass House Mountains, Mount Flinders, 

 the Nandewars, the Warrumbungles, and the Mittagong trachyte 

 area in the midst of almost horizontal Trias-Jura and Triassic 

 sediments has been explained in my former papers dealing with 

 those regions, and in Taylor and Mawson's paper on " The 

 Geology of Mittagong" (for references see later). These sedi- 

 ments are never folded to any extent except quite locally near 

 Ipswich. 



This relation even holds in far-off Antarctica, where Captain 

 Scott's expedition found the ancient complex capped by a series 

 of unfossiliferous sandstones showing the same lithological 

 characteristics as the Hawkesbury Sandstones of New South 

 Wales, viz., current-bedding, shale seams, and doleritic dykes 

 and sills Through this series, known as the Bindon Sandstones, 

 alkaline lavas have broken in places. 



The very frequent occurrence of intruded but unfolded Meso- 

 zoic beds in alkaline areas serves to show us that these parts were 

 frequently epicontinental seas in the Triassic period, and, in the 

 Jurassic and Cretaceous, marine transgressions invaded them; but 

 they were never the seat of a mighty and prolonged sedimentation 

 such as is followed by orogenic uplift and folding. 



This fact too serves to show us that the alkaline areas are 

 strictly continental and belong to those parts of the earth's crust 

 which have been for long periods affected only by cooling and 

 contraction, and never by rise of isogeotherms and the consequent 

 compression. 



The Relation of the Alkaline Areas to the Distribution of 

 Land and Sea in Past Geological Periods. 



In a previous paper I have already shown that the alkaline 

 rocks of Eastern Australia follow approximately a course which 

 has, throughout the periods of the geological record, been a 

 border zone between land and sea. Oscillations have led to 

 sedimentation alternately on the one side or the other of this 

 38 



