270 FLORA OF THE WEST YORKSHIRE HILLS. 



plants in question., viz., Armeria maritima^ Silene marifima, and 

 Plantago viaritima^ so high up on the Craven hills, is an extra- 

 ordinary one when we consider that they ordinarily thrive best 

 and are most abundant near the sea. Scientists account for their 

 presence on these elevations by the theory that the heights on 

 which they now grow formed the cHffs rising above the waters of 

 the ancient sea whose arms once filled the Yorkshire dales. Then, 

 of course, they grew in a natural environment under natural con- 

 ditions ; but, when the rising land displaced the water, they were 

 left behind, and their offspring still Hnger on where they are found 

 to-day. 



The ferns which occur so far away from their congeners are 

 the rare Aspleniu?n laficeolatum and Killarney fern, and the more 

 frequent Asplenium viride. The first grows on an old wall on the 

 moorlands near Sheffield. The next nearest station for it is in 

 Wales, one hundred miles distant. There is no record of its 

 having been introduced by human agency, and naturalists, in 

 explanation of its strange occurrence, assert that the spores from 

 the Welsh plants have been carried by the prevailing South-west 

 winds to the crannies of the old wall, where, having effected a 

 lodgment and found a congenial home, it now flourishes. 



The presence of the second — a fern, as the name indicates, 

 having its headquarters in the South-West of Ireland — is account- 

 ed for in the same way. Both of these rare ferns are of what is 

 known as the Atlantic type, and entered England from the South- 

 west at some very remote period, when there was, as geologists 

 state, a land connection between Ireland and Wales. 



The third, Asplejiium viride^ the green-ribbed Spleenwort, is, 

 except in one instance in Yorkshire, restricted to the limestone, so 

 that its occurrence at the head of the Wessenden Valley, near 

 Huddersfield, on grit rocks, away from the limestone districts, 

 though at a high altitude, puzzles naturalists very much. 



In the Islands of Bermuda there are only seven native species 

 of wild birds, while no less than one hundred and twenty-eight 

 other species pay visits to the islands. Many of these are birds 

 which pass the summer in the United States of America, and 

 utilise the Bermuda Islands as a convenient winter resort. 



