James Durham — Post- Glacial Beds at Dundee. 307 



"no trace has survived of any late deposit overlying the peat, so 

 that we cannot be absolutely sure of the position which this sheet 

 of vegetable matter would occupy if all the Post-tertiary deposits of 

 the district could be grouped in chronological order" (p. 318). 



In the face of this statement by such a high authority it seems 

 to be very desirable that the details of a section in post-Glacial beds, 

 exposed in digging the foundations of the new Post Office in Dundee, 

 should be recorded in the pages of the Geological MAaAziNE. 



As the readers of this Magazine are probably not all familiar with 

 the recent geology of the Firth of Tay, it may be well to state briefly 

 the chronology of these comparatively recent deposits heretofore 

 usually accepted. 



At the close of the Glacial Period, or at least when the glaciers 

 had mostly withdrawn from the sea-level, the land stood more than 

 100 feet lower than at present ; the floor of the sea at that time is 

 represented now by a much denuded plateau of sand and gravel, 

 and by a well-worn beach shelf, which indicates a prolonged rest 

 of sea and land at that level ; besides the sand and gravel of which 

 the plateau is mainly formed, excavations often bring to light huge 

 boulders which could only have come into their present position by 

 being floated there, which would seem to show that some of the 

 fading glaciers at times reached the sea and detached masses of ice 

 sufficiently large to float these boulders, and, melting, dropped them 

 where they are found. 



A slow but apparently uninterrupted upward movement of the 

 land then took place, until it stood about 50 feet lower than at 

 present, when another prolonged rest is indicated by a well-marked 

 beach shelf ; between that and the present sea-level the most im- 

 portant beach is that at 25 to 30 feet above the present, but between 

 these beaches there are indications of what seems to have been 

 relatively short rests in the movement. During the long time since 

 the 100 feet terrace, as it is called, was under the sea, denudation 

 has removed a very large proportion of it ; especially is this the case 

 in estuaries and river-valleys. 



In the Firth of Tay a forest grew on the denuded surface of the 

 100 feet terrace beds. This forest is represented by a bed of bluish 

 olay in which are entombed roots, trunks, and branches of trees 

 with hazel-nuts ; also fragments of insects and sometimes bones of 

 deer are found in this bed ; the nuts are much flattened, as if they 

 had been subjected to great pressure under a superincumbent load. 

 This forest bed is found at different levels all over the Firth of Tay, 

 and at some points is seen to pass under low water. This used 

 to be taken to prove that the land stood higher in the time of the 

 forest than it does now, and naturally so, as it is difficult to imagine 

 a luxuriant growth of trees and bushes flourishing fourteen feet 

 below high-water mark in this broad arm of the sea. 



In the upper parts of the Firth of Tay and the Earn another bed 

 or series of beds is found rising some 30 or 40 feet above the 

 present sea-level ; these beds consist of clay, sand, and silt, and are 

 known as the Carse Clays. 



