404 PREHISTORIC EUROPE. 



in its upper part contains no shells, but it rests upon and in 

 places seems to graduate into the fossiliferous estuarine mud 

 and sand. In a section recently exposed at a few feet above 

 high-tide mark in a railway cutting at Montrose, which I visited 

 in company with Dr. Howden, the C arse-clay is a pale yellowish- 

 gray deposit, destitute of fossils, and having all the appearance 

 of a freshwater accumulation. It rested directly upon a dark 

 grayish-blue silt and mud, which is charged with marine shells, 

 and from which a skull of the long-fronted ox (Bos longifrons) 

 was obtained. The contrast in colour and consistency between 

 the true Carse-clay and the underlying Scrobicula7'ia-sU.t was 

 very marked. 



The succession of changes evinced by these accumulations 

 appears to be as follows : — 



1st, Long after the retreat of the glacial sea, the land 

 extended considerably farther out to sea than it now does, and 

 the climatic conditions were certainly not less genial than they 

 are at present — an arboreal vegetation clothing the country. 



2d, A period of submergence ensued when the sea advanced 

 inland beyond its present limits, and reached to a height of not 

 less than 20 feet and probably as much as 45 feet above its 

 present level. Scrobicularia pipcrata an d other shells then 

 flourished in abundance in what are now the lower reaches of 

 the river Esk. 



3d, The Esk by and by carried down immense quantities of 

 fine gray and yellow silt, with which it choked up the estuary — 

 the upper reaches of which would be greatly freshened by the 

 abundant influx of river-water. It is for these reasons that the 

 Carse-clays in the upper part of the old estuary are, as Dr. 

 Howden has shown, unfossiliferous. The phenomena indicate, 

 as it seems to me, conditions quite analogous to those presented 

 by the Carse-deposits of the Tay. Local glaciers then occupied 

 the Highland valleys, and discharged large volumes of muddy 

 water during summer. 



A&li, Elevation of the land now ensued, and the sea retreated 

 to lower and lower levels, until eventually the coast extended 



