284 Reports and Proceedings — Geological Society of London. 



consecutive days, enables the author to construct a curve showing 

 the relationship existing between the rise and fall of the tide on the 

 coast and that of the water in the well. The result is to establish 

 the existence of a wave in the well of the same frequency as the 

 tidal wave, but delayed, or with an establishment of, three houra 

 {plus or minus a few minutes). 



The analyses of water taken from the well at its highest and 

 lowest show no difference, so that no sea-water enters the well 

 directly. On the other hand, the slight brackishness of the water 

 appears to prove the diifusion of a small amount of salt water into 

 the well. 



2. " Petalocnnus." By F. A. Bather, Esq., M.A., F.G.S. 

 Certain curious fan-like objects, obviously eehiuodermal, have for 



a long time been preserved in the Eiks-Museum at Stockholm, but 

 their significance was first definitely ascertained when similar fossils 

 were found in Iowa, and brought to England by Mrs. Davidson. 

 The latter were described by Mr. Stuart Weller in a paper entitled 

 " Petalocrinus mirahilis (n.sp.), and a New American Fauna"; and 

 the former, with fresh material obtained by Mr. Weller from various 

 American localities, are the subject of the present communication. 



The Silurian crinoid genus Petalocrinus, Weller, is discussed, on 

 the evidence of all the original material from Iowa and of the 

 further material above mentioned. The replacement of the original 

 material of the lowan fossils by silica has taken place only in certain 

 parts, forming a number of siliceous boxes, as it were, which are 

 either hollow or more or less filled with chalcedony or crypto- 

 crystalline silica. They are therefore neither casts nor impressions, 

 and details of structure are frequently destroyed, 



Petalocrinus is shown to have a dicyclic base — not monocyclic, as 

 originally described. The structure of the tegmen is shown to be 

 that of the Cyathocrinoidea. The arm-fans characteristic of the 

 genus are proved to have been formed by fusion of the branches of 

 an arm of Cyathocrinid type. In them, description is given for the 

 first time of axial canals, covering-plates, the articular facet, and 

 various minor structures. The species P. major, Weller, is shown 

 to be an Omphyma ; but P. mirahilis, Weller, the genotype, is re- 

 described, and with it five new species — two from Iowa ; three, as 

 well as a possible mutation of one of them, from Gotland. A family 

 Petalocrinidae, descended from the Cyathocrinidse, probably by way 

 of Arachiocrinus, is founded for the reception of this genus. 



3. "On the Origin of the Auriferous Conglomerates of the Gold 

 Coast Colony (West Africa)." By Thomas B. F. Sam, Esq., CE. 

 (Communicated by J. Logan Lobley, Esq., F.G.S.) 



This paper gives an account of a recent journey from Adjah Bippo 

 to the Ankobra Junction in the Gold Coast Colony. A range of 

 clay-slate hills is succeeded for six miles by flat ground in which 

 diorite was found, and that by a lofty hill in which clay-slate dipping 

 east occurs. The Teberibie range with reefs of conglomerate, and 

 a second range with similar reefs, were crossed. 



