BRITISH POSTGLACIAL & RECENT DEPOSITS. 387 



terrace, which may be traced often for miles along the slopes of 

 the valleys. They fringe most of the so-called Inches in the 

 Carse of Gowrie, and spread out in broad sheets and plains in 

 the Earn valley above Eorgandenny, and in that of the Tay a 

 little to the north of Old Scone. Their upper surface, as I have 

 said, is just 100 feet above the sea-level, and they maintain the 

 same level all the way from near Dundee to some miles above 

 Dalreoch in the valley of the Earn, and to Luncarty above 

 Perth in that of the Tay. But when we trace them farther in- 

 land, we find they gradually rise in elevation and pass into flats 

 and terraces of river-gravel and sand. Judging, therefore, merely 

 from the mode of their occurrence, we should say that the depo- 

 sits of the 100-feet terrace were of estuarine formation. In the 

 upper reaches of the valleys they consist principally of gravel, 

 shingle, and sand, but in the wider and opener areas they are 

 made up to a large extent of brick-clay, which is usually finely 

 laminated, and often contains scattered stones and large erratics. 

 Along the margin of the deposits such large erratics occur here 

 and there in great abundance. Near Errol, in a brick-clay be- 

 longing to the series under review, marine shells have been 

 obtained in considerable numbers. They belong to species which 

 are now characteristic of high northern latitudes, and include 

 such extremely arctic forms as Pecten grmnlandims, Leda arctica, 

 Tellina myopsis, etc. 



From these facts we gather that after the disappearance of 

 glacier-ice from the lower valleys of the Earn and the Tay, the 

 sea encroached upon the land, and reached to a height of 100 

 feet or so above its present level. The climate was still very 

 cold ; glaciers probably continued to occupy the upper reaches 

 of the valleys ; and great bodies of muddy water derived from 

 the melting snow and ice flooded the low grounds in summer, 

 and swept down to the estuary heaps of shingle, gravel, and 

 sand. Similar freshets descending from small lateral valleys in 

 the Ochils formed great cdnes de dejection of detritus, as they 

 escaped from their gullies to mingle their waters with those 

 of the estuary. Much river- ice, carrying gravel, stones, and 



