Boulder Clay — A Marine Deposit. 53 



deposited at a time when an Arctic climate prevailed 

 somewhat similar to that at present existing in Spitzbergen. 

 But geologists were not so unanimous in their theories explain- 

 ing its formation, some holding that it was the result of the 

 action of land ice, and others that it was of marine origin. 

 Special attention had been given to this subject by geologists 

 in the North of Ireland. Major-General Portlock's opinion was 

 that these clays were of marine origin, and in his report on the 

 geology of Londonderry, published in 1843, he gave a list of 

 fossil shells found by Messrs. Brien and Hyndman in boulder 

 clay which was cut through when the reservoir for the Belfast 

 Waterworks was being excavated. Mr. S. A. Stewart, the 

 curator of the Museum, published in t88o a hst of mollusca 

 from Irish boulder clay, in which he recorded sixty-nine species 

 of shells. Examples of Leda permula and Leda pygmcea were 

 obtained both at Woodburn and the Knock with their valves 

 attached, which proved that they must have lived on the spot 

 where found. Mr. Wright then proceeded to describe his 

 examination of boulder clay from the vicinity of Glasgow, and 

 expressed his indebtness to Mr. James Nelson, vice-president 

 of the Glasgow Geological Society, for his kindness in supplying 

 him with samples of typical Scottish boulder clay. Material 

 from eleven different localities had been examined, and in all of 

 these foraminifera were found. These specimens were all of 

 the same species as those found at present in shallow water off 

 the Irish coast, and, with the exception oi discorbina parisiensis, 

 had all been found in Irish boulder clay. Rotalia beccartt, 

 nonionina depressula^ and polystonidla striata punctata were 

 the most abundant in the clay, and the same species were the 

 most common amongst our shallow-water forms. Mr. Wright 

 concluded by saying that the result of his examination of both 

 the Scotch and Irish boulder clays, and the finding in them of 

 many shallow-water organisms, forced him to the conclusion 

 that the boulder clay both in Scotland and Ireland was of 

 marine origin. 



