282 THE SCOTTISH NATURALIST 



and to establish the northern range of the smaller and more 

 inconspicuous ones more extended investigation is requisite. 



It appears worthy of remark that the present knowledge 

 of the northern limits of these forms corresponds fairly 

 closely with the existence of that outstanding physical 

 feature of the Highlands, the immense rift or great glen, 

 through which the Caledonian Canal runs in a perfectly 

 straight line, obliquely from north-east to south-west, a 

 feature which is of immense geological age, an arm of the 

 sea in Jurassic and Liassic times, and still a depression in 

 the Triassic age. This, if it be a barrier to the northern advance 

 of the dominant species mentioned, has only been passed 

 at one single point (Ardtornish) by one of these species, H. 

 aspersa, thus opening the way to their colonisation of the 

 northern Highlands, an extension of range which the 

 inhospitable character of the country only can delay. 



A problem which needs close investigation is the reported 

 occurrence of Pyramidula rupestris at Durness, in the 

 extreme north-west of Sutherland, so far removed from its 

 known range to Perth and Oban that it is very necessary 

 for the locality to be closely examined. 



Of matters subsidiary to the main object in view, may 

 be mentioned the possibility of finding such species as 

 Acanthinula Jiarpa and Pyramidula rudcrata, which occur 

 in regions in Europe which can only be paralleled in 

 Britain by the Scottish Highlands ; but so far neither has 

 been observed in these islands, except the latter in a fossil 

 state. 



The continuance of the investigation in the country 

 north of the great rift of the Caledonian Canal is urgently 

 necessary for the completion of the task, and it is hoped 

 that a further grant may be forthcoming for the exploration 

 of the extreme north coasts of Sutherland and Caithness. 



