518 Geological Society. 



lands, by which the gravel of Forfar was uplifted, or the till to the 

 northward depressed. 



Another line of stratified detritus ranges at a higher level from 

 the Loch of Lundie, along the Dichty Water, to the sea at Moray 

 Firth, a distance of thirteen miles ; and it is stated that many others 

 might be enumerated. It is only on the coast to the east and west 

 of Dundee, at heights varying from twenty to forty feet, that strati- 

 fied clay and gravel have been found by Mr. Lyell to contain marine 

 shells, all belonging to known existing species, except a Nucula. 

 Although these remains prove a certain amount of upheaval subse- 

 quent to the deposition of the till, or to the commencement of the 

 glacial epoch, including an equal movement in the interior, still 

 Mr. Lyell objects to a general submergence of that part of Scotland, 

 since the till and erratic blocks were conveyed to their present 

 positions ; as the stratified gravel is too partial and at too low a 

 level to support such a theory ; and he would rather account for the 

 existence of the stratified deposits, by assuming that barriers of 

 ice produced extensive lakes, the waters of which threw down 

 ridges of stratified materials on the tops of the moraines. With re- 

 spect to the geological age of the beds containing the marine shells, 

 Mr. Lyell is of opinion that it is synchronous with that of the 

 older of the recent formations on the Clyde, examined by Mr. Smith 

 of Jordan Hill, and Mr. E. Forbes ; and with respect to the age of 

 the till and stratified gravel last formed, he is of opinion that it is 

 A'ery modern, because these accumulations constitute exclusively the 

 dams of certain marl-lochs to the very bottom of the sediment 

 formed, in which all the Testacea and skeletons of quadrupeds, as 

 well as the remains of plants which have been found, are of existing 

 species. 



The third district, or that of the Sidlaw Hills, claimed Mr. Lyell's 

 attention more particularly on account of the Grampian boulders 

 with which it abounds. This range, whose greatest height is 1500 

 feet above the sea, is composed of anticlinal strata of grey sandstone, 

 belonging to the old red sandstone, with associated trap. It is co- 

 vered, as well as the whole of the country between Strathmore and 

 the Tay, with the impervious till, containing Grampian boulders and 

 fragments of the subjacent grey sandstone. The finest instances of 

 en-atics observed by Mr. Lyell occur on Pitscanly Hill, 700 feet, and 

 the adjacent hill of Turin, 800 feet above the level of the sea. About 

 forty feet below the summit, on the southern side of the former, is 

 a block of mica-slate thirteen feet long, seven broad, and seven in 

 height above the ground. Four smaller and equally angular masses, 

 from three to six feet in diameter, lie close to its north end, as if se- 

 vered from it. One of the nearest points at which this gneiss occurs 

 in situ, is the Craig of Balloch, fifteen miles distant, on the northern 

 extremity of the Creigh Hill, and between these points intervenes 

 the great valley of Strathmore and the hills of Finhaven. Other 

 Grampian boulders, from three to six feet in diameter, occur on the 

 hills between Lumley Den and Lundie, at the height of 1000 feet ; 

 and Mr. Blackadder has found fragments of mica- schist one foot in 



