8 



In relation to the discovery, Dr. Cliewings writes from 

 Arltunga (September 12, 1912) : "You will be interested to 

 know that I made what I take to be a very important dis- 

 covery of probably Cambrian fossils the other day, in the 

 MacDonnell Ranges. They occur for several miles in a massive 

 limestone (dolomite) range that skirts the gneissic and granitic 

 formation of the Central MacDonnell." 



The following is a sketch supplied by Dr. Chewings to 

 show the stratigraphical relationship of his discovery to the 

 f ossiliferous Ordovicians of the same ranges : — 



SKETCH SECTION OF CENTRAL MACDONNELL RANGES 



(Chewings). 



A. Gneissic and Granitic (? Pre-Cambrian). B. Quartzite 

 (? Cambrian). C. Dolomitic Limestone (? Cambrian); Cryptozoon 

 fossils at xx. D. Ordovician fossils at x x . 



''The Ordovician beds (D), with fossils, occur as shown 

 on the rough section. The 'inner' quartzite and limestone 

 beds (B and C) I have always held to be older, but could 

 never find fossils in them until now/' — [Chewings.] 



In a further letter, dated October 5, 1912, from Charlotte 

 Waters, he writes : "The quartzite runs the whole length of 

 the MacDonnell Ranges, viz., from beyond Mount Udor to 

 east of Arltunga, sometimes in broken and isolated hills, at 

 others in a continuous line or lines forming the highest range 

 of the MacDonnell. The dolomite I know to extend from 

 Mount Giles to east of Arltunga, and, like the quartzite, 

 is always very much disturbed, broken, and thrust about. 

 It has undergone such disturbance and alteration that all 

 trace of fossils has, in most parts, disappeared. Where the 

 fossils were found the dolomite is of great thickness, and for 

 a couple of miles, in one place, viz., near Acacia Well, which 

 lies south of Mount Benstead, and in another, viz., two miles 

 south of Bitter Springs, the fossils escaped obliteration. The 

 two spots are five miles apart. Where the samples were 

 found there is no lack of similar material, the rock being 

 largely composed of the same coralline rock, or what origin- 

 ally were corals. Where the fossils occur the dolomite beds 

 dip south, at say, So ." 



