former existence of Glaciers in Forfarshire. 585 



appears to offer a hajiin' solution of the problem of the marl-locli 

 gravels, the longitudinal banks being regarded as lateral and medial 

 moraines, and the transverse ridges as terminal. The chief ol)jec- 

 tions Eire the stratification of tlie upper part of the banks, and the 

 necessity of assuming a glacier tliirty-four miles in length, -with a 

 fall of only 300 or 400 feet of country. 



It has always appeared to Mr. Lyell and Mr. Blackadder remark- 

 able, that the marl-loch gravels at Forfar are nearly 100 feet above 

 the tract of till which separates them from the valley of South Esk, 

 in Strathmore. In the present configuration of the country, water 

 could not deposit the Forfar gravels without extending to the South 

 Esk, the detritus of which is distinct, and separated by a low district 

 of till without gravel. The only exj^lanations of these phenomena 

 Mr. Lyell considers to be either that the till is the moraine of a 

 glacier, or that there has been a local change of relative levels of 

 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. Lj'cU 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 jiartial 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 

 very 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 quadrujieds, 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. Ihis range, whose greatest height is 1500 

 feet above tlie 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 



