Vol. 56.] 



LIMESTONES FROM KATHIAWAK, ETC. 



577 



Fiff. 4. 



PART OF GALWAY 



SCALE = UNE INCHTO A MILE 



The surface- drift in the North Atlantic, doubtless with the assis- 

 tance of local currents, brings a plentiful supply of foraminifera 

 into Dog's Bay, and every high tide spreads them over the gently 

 sloping strand, where they are associated with numerous small 

 gasteropoda (Rissoa) and other larger shells. In fine, warm weather 



they rapidly dry, and 

 are carried landward 

 by the wind before the 

 tide again advances. 

 Sometimes, when a 

 slight shower has 

 washed the minute 

 calcareous particles 

 free from salt, almost 

 the whole surface of 

 the strand may be 

 seen moving steadily 

 up beyond high water, 

 rolling into and filling 

 any hollows in the 

 path with pure wind- 

 drifted foraminifera 

 and ostracoda (mostly 

 snowy- white) and finely comminuted shells. In high winds much of 

 the foraminiferal material is blown right across the isthmus to 

 Gorteen-Bay strand and into the sea beyond, where it can be 

 sometimes seen floating upon the surface of the water. 1 



The foraminifera of Dog's Bay are not surrounded by an envelope 

 of deposited carbonate of lime : hence we may draw the conclusion 

 that the water in the bay was not saturated with it ; and whatever 

 may be the case at other places, there is not here a subaqueous 

 deposit forming in the bay similar to that accumulated by wind- 

 .action on the isthmus, for the continual movement of tidal currents 

 would be sufficient to keep the foraminifera in motion until they 

 were dissolved. 2 



An ancient beach made up of foraminifera and comminuted 

 shells, with rounded fragments and pebbles of non-calcareous rocks, 

 was described by Prestwich from Barnstaple Bay, and seems to 

 represent an ancient deposit similar to that at Dog's Bay. It is 



%M W.inrihinwn Calcareous Deposit 



1 This description is extracted from Mr. Welch's letters to me. He briefly 

 refers to the subject in a paper on ' Land-Shell Pockets on Sand-Dunes ' 

 [40]. The foraminifera are enumerated by Mr. Joseph Wright [37], and 

 Messrs. Standen & Collier have dealt with the mollusca [38 & 39] from the 

 same locality. The isthmus is mapped by the Geological Survey of Ireland 

 as blown sand [34]. In the accompanying memoir [35] we read : ' Some of 

 the meteoric drift is represented by tracts of aeolian or blown sand, both 

 siliceous and calcareous. This occurs principally near the coast, but it is also 

 found in some of the inland valleys.' 



2 It is true that the foraminiferal tests washed ashore have arrived practically 

 uninjured from a long sea-journey, but they were probably protected by organic 

 material still adherent to them. 



