338 PROCEEDINGS OF THE 



as the upper one, would require further investigation. The 

 organisms got in the lower shell-bed are all of a dwarfed character. 

 The same species appear in the upper bed, but a great many of 

 those got here do not appear in the lower shell-bed. What may 

 be the entire depth of this clay-field I am unable to say, but from 

 the journal of bores taken in the neighbourhood of Houston and 

 Johnstone, there appears to be a great depth of laminated and 

 boulder clay ; one bore gave more than 90 feet of soft muddy 

 clay, with about 3 feet of till and stones on the rock head At 

 Walkinshaw, within a mile or so, numerous bores prove a great 

 depth of surface, sometimes as much as 160 feet, and 90 to 100 

 feet is common. The most of these bores have muddy clay 

 extending the whole depth. Some few have 30 or 40 feet of 

 boulder clay at the bottom, capped by double that thickness of 

 muddy clay. In two or three bores boulder clay extends from top 

 to bottom, being more than 100 feet. From these facts it is clear 

 that the muddy clay lies in hollows in the boulder cla}'-, which is 

 evidently an older formation. It is not likely, considering the 

 circumstances of its formation, that this boulder clay was formerly 

 uniform in thickness, still I believe that it extended more 

 generally over the rock surface than is now the case, and that it 

 must have suffered much denudation ere the deep hollows were 

 formed in which the muddy clay is deposited. But how^ever these 

 hollows may have been formed, there can be little doubt that the 

 beds of muddy clay, now lying in and over them to a depth of 

 100 to 130 feet, were formed in the sea. 



It may be interesting here to consider how some of these changes 

 were effected, and to endeavour to trace out what may have been 

 the course of events. It is clear that the greater part of the 

 glacial period had passed ere the clays containing Arctic shells 

 were laid down. The great mass of boulder clay lying below them 

 proves this, and it is probable tliat even the severest cold had given 

 place to a comparatively milder temperature. The land and sea 

 had changed places, or rather a moderate submergence had 

 brought the sea over all the lower parts of Clydesdale,' and land 

 ice had given place to sea water. This comparatively shallow 

 sea extended from the Gleniifer braes on the south, to the 

 Lennox hills on the north, and from Bowling to Bothwell, receiving 

 directly the drainage of the country surrounding, on the north and 

 south, and that from the east was doubtless poured into it by a 



