BY T. W. EDGEWORTH DAVID. 563 



The limestones have been considerably altered by contact with 

 the New England granite. The claystones and cherty rocks both 

 above and below the limestones have also been much altered by 

 innumerable granite sills for a zone over five miles in width, 

 measured at right angles to the junction line between the 

 sedimentary rocks and the granite. A lamination, coincident 

 with the planes of bedding, has been superinduced in the clay- 

 stones. The sills vary from a fraction of an inch up to several 

 feet in thickness, and at first sight had every appearance of lieing 

 regulai'ly interstratified with the sediments. A careful examina- 

 tion, however, at once revealed their intrusive character, as they 

 trespass slightly across the planes of bedding and ha\e slightly 

 altered by indurating and develoi:)ing chiastolitic minerals, the 

 sedimentary rocks both above and below them. The claystones 

 and cherts dip chiefly westwards at angles of from 45 to 60°. At 

 Tamworth Common the dip is W. 20° S. at 52°. Radiolaria are 

 abundantly distributed through these claystones and cherts in 

 the form of chalcedonic casts. Associated with the claystones is 

 the siliceous calcareous rock previousl}' referred to. A good 

 section shewing it in situ is exposed at tlie quarries on the Tam- 

 worth Temporary Common. The chief bed is about 18 inches in 

 thickness. It weathers superficially into a soft brown friable 

 rock of the colour of Fuller's earth, much resembling bath-brick. 

 Fresh fractures, of unweathered portions, shew the rock to be 

 bluish-grey and compact. If a surface of the unweathered portion 

 be smoothed and polished and then etched with dilute hydro- 

 chloric or acetic acid, interstitial carbonate of lime is dissolved 

 out, and well preserved siliceous shells of radiolaria become visible. 

 These will be described in detail later. A second bed of siliceous 

 radiolarian limestone occurs at a point about a mile easterl}' from 

 the pi-eceding. It is a few inches onh' in thickness. For the 

 general appearance of this rock see Plate xxxvii. The radiolarian 

 rocks are probably at least 2000 feet thick at Tamworth. The 

 distance from Bingera on the north to Tamworth on the south is 

 85 miles. Barraba, intermediate between these two places, is 34 

 miles south of Binicera and 51 miles north of Tamworth. The 



