343 
the successive rise of the land. They usually consist of stratified 
sand and gravel, the layers being often at high inclinations; but 
where they are composed of boulders, no stratification is observable. 
After a long search, Mr. Lyell succeeded in finding shells m a layer 
of marl belonging to a ridge in the suburbs of Upsala, about twelve 
feet below the summit of the ridge, and eighty above the sea. The 
shells consisted of Mytilus edulis, Cardium edule, Tellina Baltica, 
Littorina littorea, and Turbo ulve, the most common species in the 
Baltic, and they constituted the greater part of the layer. On the 
summit of the ridge, at a short distance, he noticed angular masses 
of gneiss and granite, from nine to sixteen feet long, which had 
evidently been lodged when the ridge was submarine. 
In Forfarshire Mr. Lyell never succeeded, as in the above case in 
Sweden, in finding marine shells in the ridges of sand; nor does he 
remember to have seen in Sweden transverse ridges at right angles 
to the north and south. The glacier theory, the author states, 
appears to offer a happy solution of the problem of the marl-loch 
gravels, the longitudinal banks being regarded as lateral and medial 
moraines, and the transverse ridges as terminal. The chief objec- 
tions are the stratification of the upper part of the banks, and the 
necessity of assuming a glacier thirty-four miles te length, with a 
fall of only 300 or 400 feet of country. 
It has always appeared to Mr. Lyell and Mr. Bluclsidllen 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 explanations 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. 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 lowa 
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- 
VOL. I1I.—PART II. 25 
