7 16 Proceedings of the Royal Irish Academy. 



An examination of the present distribution of the above species shows 

 that all are very common in the British and Irish Seas at the present day, 

 and that their presence in the boulder-clay of Clare Island throws no light 

 on the climate of western Ireland during Glacial times. It was decided to 

 see if the great development of drift around Clew Bay would yield more 

 definite information. The coast-line around the bay was searched without 

 any shells being found. In 1881 the Geological Survey had reported shelly 

 drift in North Mayo near Ballycastle, and Canon Grainger had named eight 

 species from the collection made. Two of these eight species were arctic 

 types ; and Ballycastle being only about twenty-five miles to the northward, 

 it was decided to see what fresh information could be obtained by a careful 

 examination of these deposits. The coast-line of North Mayo was examined 

 from Lacken Bay to Port Urlin, and the shelly drift was found to be confined 

 to the coast between Glenulra and Belderrig. The district is one in which 

 ice-movement was apparently of frequent occurrence, and at least three 

 boulder-clays were distinguished. These were as follows : — 



1. In Glenulra and Owenbehey occurs a blue till (the "blue mud " of the 

 district) with a great number of shell-fragments. The following species were 

 recognisable : — 



Lamellibranchiata : — Ostrerc edulis Linn., Mytilus sp., Nuculana (Leda) 

 pernula 0. F. Miiller, Cardium edule Linn., Cyprina islandica Linn., Astarte 

 borealis Chem., Tellina balthica Linn., Corbula sp., Glycimeris (Panopea) 

 norvegica Speng., Mya truncata Linn. 



Gasteropoda : — Turritella communis Bisso, Purpura lapillus Linn. 



Cirripedia : — Balanus sp. 



2. From Lackan Bay to Port Urlin the greater part of the country is 

 covered with a brown boulder-clay which contains shell-fragments when it 

 rests on the denuded surface of the blue till. 



3. At Belderrig, and for about a mile to the eastward, occurs a calcareous 

 boulder-clay much less tough than the blue till, and apparently resting on the 

 denuded brown boulder-clay. In addition to many of the blue-till species 

 this boulder-clay is made very important by the presence in large numbers of 

 the well-known northern form Tellina lata (known also as Tellina proximo, 

 and Tellina calcarea). The individual valves of this shell are very well pre- 

 served, the epidermis being retained in many cases. This shelly drift of north 

 Mayo is very important, as showing that, judged by the present distribution 

 of mollusca, the species found in these drifts indicate a lowering of the tem- 

 perature, Astarte borealis, Leda pernula, and Tellina lata, being distinctly 

 northern forms. A more extensive account of these north Mayo shelly drifts 

 will be found in the " Irish Naturalist," vol. xxii (1913), pp. 1-6, 



