342 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



scribed as occurring at a height of about 5 feet above high water 

 mark. The shells are numerous and broken, and they are associated 

 with concretions of carbonate of lime. The author considers that 

 this deposit may have been formed at a time when the valley of 

 the Colne was an estuary of the neighbouring sea. The shells are 

 all those of the common recent species found on the coast, but 

 the bed is now ten miles distant from the sea. 



The author considers that the perfect state of the shells in these 

 cases precludes the possibility of their having been drifted, and 

 that they therefore afford sufficient proof of the general level of 

 this part of the British coast having undergone a small elevation at 

 a recent geological epoch. 



2. On Dykes of Marble and Quartz in connection with Plutonic 

 Rock on the Upper Wollondilly in Argyle County, New 

 South Wales. By the Rev. W. B. Clarke, M.A., F.G.S. 



The tract of country described by the author in this memoir is 

 situated not far from Sydney and Port Jackson, the river Wollon- 

 dilly, whose gorge lays bare the geological structure of the district, 

 taking its rise in latitude 34° 26' $., longitude 149° 23' E., and 

 after receiving the waters of several streams running into the 

 Nepean river, and emptying itself into the Ocean considerably to 

 the south of Sydney.] 



The stratified rocks traversed by the remarkable defiles through 

 which these rivers flow, belong to the sterile upper portions of the 

 carboniferous formation so widely spread in Australia ; and these 

 carboniferous rocks are traceable (with occasional interruptions 

 from basaltic dykes) from the district in question to the borders 

 of the Illawarra region, where they present a lofty mural escarp- 

 ment. 



The Wollondilly, however, from its source to its junction with 

 the Uringalla (except near Towrang), is described by the author 

 as running through igneous and metamorphic rocks, which are 

 laid bare over a considerable area between the Cockburndoon, the 

 Derra, and the Uringalla rivers, where recent volcanic outbursts 

 have disturbed the older rocks. The sedimentary rocks wrap 

 round the margin of this area, the beds dipping at a considerable 

 angle. 



On the north banks of the river, at a place called Jaoramin, 

 beds of conglomerate are described containing fragments appa-* 

 rently of transition rock ; and the author considers, from the con- 

 dition and appearance of the river banks, and the fact that a wide 

 space, at a considerable height above the water, is covered with 

 the debris of these conglomerates, that a considerable change of 

 level has taken place in the district producing elevation. 



Having given a general account of the districts, the author then 



