1820.] Geological Society. 67 



In a former paper, M. de la Beche gave an account of the 

 fossil animal fomid in the blue lias of Lyme, usually called the 

 ichthyosaurus, but which has been lately named by Sir E. Home 

 the proteosaurus ; the object of these additional remarks is to 

 point out several species of proteosaurus which have been disco- 

 vered. These are three : the communis, the tenuirostris, and 

 the pliityodon. The characters of the species are taken from the 

 form of the teeth and the jaw bone, and the names of the tv/o 

 latter are derived from the shape of these parts. There are 

 probably other species, but they are not yet sufficiently well 

 ascertained. 



The author gives, from Dr. Leach, a scientific description of 

 the Dapedium politum, a fish with rectangular scales, that has 

 been discovered in the lias of Lvme. 



JSlov. 5.— The reading of Mr. Weaver's paper " On the Geolo- 

 gical Relations of the Environs of Tortworth, and the Mendip 

 Range in Somersetshire," was continued. 



Nov. 19.— A paper, from Dr. Nugent, was read, entitled 

 " Sketch of the Geology of Antigua." It was accompanied by a 

 map, sections, and specimens. 



The author observes that Antigua contains no marks of 

 modern volcanic action ; but many effects of former revolutions. 

 The south and east parts of the island exhibit recent beds of a 

 peculiar calcareous formation, probably cotemporary with those 

 around Paris, and in the Isle of Wight ; the surface of these 

 calcareous beds is in the form of rounded hills, like those of the 

 chalk district of England, the highest being about 300 or 400 

 feet above the ocean. The materials of this formation are not 

 uniform ; a great part of it consists of closely compacted marl,^ 

 of a brig-ht yellow colour. Through this marl run layers of 

 compact limestone containing shells, calcareous spar, quartz, 

 chalcedony, and agate. Strata of gritstone also run through 

 the marl, composed of quartz, hornblende, jasper, hornstone, 

 and green earth, held together by an argillaceous cement ; this 

 is used in masonry. The marl also contains a smooth-grained 

 calcareous sandstone, which is employed for building. The 

 calcareous formation contains many shells and corallines, both 

 calcareous and silicified ; most of them are analogous to those 

 in the neighbouring sea, but it is probable that they have been 

 deposited in their present situation at a remote period. 



The marl contains very great quantities of a substance called 

 ground pearl, the nature of which is not well ascertained. The 

 marl also contains both marine and fresh water remains, but they 

 are mixed together ; the silicified and agatized corallines, which 

 are so abundant and so beautiful in Antigua, are very plentiful in 

 the calcareous beds ; they contain no remains of large animals, 

 and no gypsum. Below the calcareous formation, and lying 

 south of it, are extensive irregular masses of coarse flint or chert. 

 They contain a large quantity of shells, chiefly cerithea, filled 



