222 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



down by currents from the River Forth, in suspension, the 

 former, however, being the chief factor from which these deposits 

 owe their origin. 



They consist for the most part of blue-grey or brown plastic 

 sandy muds, of fine grain ; along the north channel to the 

 May Island these merge into brown sandy mud, with dead shells 

 or shell sand, to siliceous sands, and from these to sand and 

 stones, shingle or rock fragments, the latter forms being found in 

 depths less than 10 fathoms, in and off bays, close inshore along 

 the coast to the low-water mark. A well-marked reach of dark 

 grey and brown unctuous mud extends from within four miles east 

 of Inchkeith, spreading out north and south, funnel shaped, to 

 within a short distance of ' the May Island, varying in depths 

 from 20 to 30 fathoms. About a mile further east it merges into 

 the grey muds or oozes of the North Sea, coloured grey on 

 the reference chart. 



On the north and south side of this area we find sandy muds, 

 with dead shells, predominating, especially over the area of 

 Stations I. and III. ; from 18 to 10 fathoms they become more 

 mixed and sandy, while between 10 and 5 fathoms and less they 

 emerge into siliceous sands, with stones and rock fragments. At 

 one or two localities, especially off St. Monance, Station VI., in 

 10 to 18 fathoms, we find a more or less pure shell sand, 

 containing from 30 to 70 per cent, of carbonate of lime (see 

 reference chart). It should be noted that coal, coal ash, and 

 clinkers have been taken, in more or less quantities, in all the 

 deposits examined from the Firth of Forth. 



Summary of the Deposits. 



The deposits obtained at Stations I. and III. are similar in 

 composition, and to them the name " Turritella Mud" might 

 appropriately be applied, on account of the great number of the 

 dead shells of the genus bearing that name it contains, and 

 and from which the high percentage of CaCog is chiefly due. 



A thin surface layer of brown fine argillaceous matter, in 

 which the Turritella lay imbedded, is of a recent formation, and a 

 striking feature over the whole floor of the firth, like in composi- 

 tion to a river mud, derived partly from material carried down 

 from the River Forth and partly from matter thrown over from 



