I860.] .TAMIESOX DRIFT, AlJERBEEXsniRE. 301 



in the lower part of the section, and are composed occasionally of an 

 impalpable mud, like putty. No trace of shells occurred to me, 

 although I searched for them narrowly in several parts. Some of the 

 fine sandy matter, when examined through a magnifying lens, was 

 seen to consist chiefly of small rounded grains of quartz, together 

 with an impalpable powder of apparently decomposed felspar. 



There were no beds of clean-washed gravel or shingle — all was 

 more or less earthy ; neither was there a great thickness of pure 

 clay in any part; and the general tone of the whole was very similar 

 throughout, varying from pale ycllo wish-grey to brown. I observed 

 that some of the finer loamy seams had been partially washed away 

 before the deposition of the superincumbent layers. 



The topmost stratum of this bank consisted of a coarse)', stonier 

 mass, 3 to 5 feet thick, which seemed to me to have resulted from 

 the denuding agency that had swept away the drift; for it differs 

 from the subjacent beds chiefly in having the finer matter washed out. 

 The stones so plentifully dispersed in the drift consisted for the most 

 part of mica-slate and gneiss, together with some of granite, horn- 

 blende, porphyry, and crystalline limestone. 



Now, as this great bank of earth contains probably several thousani Is 

 of fine laminoe. of clay and sand imposed one above another in regular 

 succession, separated by many beds of a coarser description, I think the 

 notion of such a mass having been thrown together by any sudden con- 

 vulsion becomes inconceivable, while the fact of its upper limit over- 

 topping all barriers between it and the sea is equally decisive against 

 a fresh-water origin ; and, furthermore, that its whole structure be- 

 longs to the latest tertiary period is shown from its reposing through- 

 out its entire extent on a glacially polished rock-surface. Here, 

 then, we have — 



1 . A gradual formation. 



2. A marine origin. 



3. A Pleistocene age. 



And thus I think there are proofs that in these later times the sea- 

 waters had assuredly rolled for many centuries over the hills and 

 valleys of Scotland. 



If I am correct in assuming, from its horizontal stratification, (hat 



Fig. 10. — Section across ffu Tummel Valley at Meal Uaine. 



E. W. 



ft. Top of Meal Uainc. b,b. Boulden of granite and porphyry. ,-. Bed of Drift. 



d, d. stria; on the rock. e,e. Water-rolled gravel. /. The Tummel. 



the deposit of which this bank is a portion had originally extended 



all across the valley, then it is evident what an enormOUS ■ 1< -u i nl:i t i< >n 



has taken place; for we have her,. i m t q patch, which owes it- pr 



VOL. XVI. — PAST I. L' i. 



