383 



NATURE 



\Ajigtist 26, 18S0 



Carboniferous rocks of Moscow, and having passed through the 

 latter he find-; Iiimself suddenly in a yellow-coloured region, 

 entirely dis-imilar in structure to what he had seen in any of the 

 northern governments, which, of a different type as regards 

 fossils, is tlic true stratigraphical equivalent cf the Old Red 

 system." This seems to me, as regards the Russian strata, to 

 mean that just as the Devonian strata of Devonshire are the true 

 equivalents of the Old Red Sandstone of Wales and Scotland, 

 they were deposited under very different conditions, the first in 

 the sea and the others in inland fresh-water lakes. At the time 

 Sir Roderick Murchison's work was completed, the almost universal 

 opinion was that tlie Old Red Sandstone was a marine formation. 

 In the year 1830 the Rev. Dr. Fleming of Edinburgh read a 

 paper before the Wernerian Society in which he boldly stated 

 that the " Old Red Sandstone is v^ fresJi-waler formation" of 

 older date than the Carboniferous Limestone. This statement, 

 however, seems to have made no impression on geologists till it 

 was revived by Godwin-Austen in a memoir " On the Extension 

 of the Coal-measures," &c., in the Journal of the Geological 

 Society, 1856. Even this made no converts to what was then 

 considered a heretical opinion. I have long held Dr. Fleming's 

 view, and unfortunately published it in the third edition of " The 

 Physical Geology and Geography of Great Britain," without at 

 the time being aware that I had been forestalled by Dr. Fleming 

 and Mr. Godwin-Austen. 



To give anything like a detailed account of all the fresh-water 

 formations deposited in estuaries and lakes from the close of the 

 Old Red Sandstone times down to late Tertiary epochs is only 

 fitted for a manual of geology, and would too mucli expand this 

 address ; and I will therefore give little more than a catalogue of 

 these deposits in ascending order. 



In the Coal-measure parts of the Carboniferous series a great 

 liroportion of the shales and sandstones are of fresh-water origin. 

 This is proved all over the British Islands by the shells they 

 contain, while here and there marine interstratifications occur, 

 generally of no great thickness. There is no doubt 'among 

 geologists that these Coal-measure strata were chiefly deposited 

 under estuarine conditions, and sometimes in lagoons or intakes, 

 while numerous beds of coal formed by the life and death of 

 land plants, each underlaid by the soil on which the plr.nts grew, 

 evince the constant recurrence of terrestrial conditions. The 

 same kind of phenomena are characteristic of tlie Coal-measures 

 all through North America, and in every country on the continent 

 of Europe, from France and Spain on the west to Russia in the 

 east, and the same is the case in China and in other areas. 



In Scotland, according to Prof. Judd, fresh-water conditions 

 occur more or less all through the Jurassic series, from the Lias 

 to the Uppei' Oolites. In England fresh-water strata, with thin 

 beds of coal, are found in the Inferior Oolite of Yorkshire, and 

 in the middle of England and elsewhere in the Great Oolite. 

 The Purbeck and ^Wealden strata, whicli in a sense fill the 

 interval between the Jurassic and Cretaceous series, are almost 

 entirely formed of fresh-water strata, witli occasional thin marine 

 interstratifications. By some the Wealden beds are considered 

 to have been formed in and near the estuary of a great river, 

 while others, with as good a show of reason, believe them to 

 have been deposited in a large lake subject to the occasional 

 influx of the sea. 



In the eastern part of South Russia the Lias consists chiefly of 

 fresh-water strata, as stated by Neumayr. 



The Godwana rocks of Central India range from Upper 

 Palaeozoic times well into the Jurassic strata, and there all these 

 formations are of fresh-water origin. Fresh-water beds with 

 shells are also interstratified with the Deccan traps of Cretaceous 

 and Tertiary (Eocene) age, while 2,000 feet of fresh-water sands 

 overlie them. 



In South-Western Sweden, as stated by Mr. Bauerman, "the 

 three coal-fields of Iloganas, Stabbarp, and Rodinge lie in the 

 uppermost Triassic or Rhajtic series." In Africa the Karoo 

 beds, which it is surmised may be of the age of the New Red 

 Sandstone, contain beds of coak In North America certain 

 fresh-water strata, with beds of lignite, apparently belong to the 

 Cretaceous and Eocene epochs, and in the north of Spain and 

 south of France there are fresh-water lacustrine formations in 

 the highest Cretaceous strata. 



In England the Lower and Upper Eocene strata are chiefly of 

 fresh-water origin, and the same is the case in France and other 

 parts of the Continent. Certain fresh-water formations in Cen- 

 tral Spain extend from the Eocene to the Upper Miocene strata. 



There is only one small patch of Miocene beds in England, at 

 Bovey Tracey, near Dartmoor, formed of fresh-water deposits 

 with interstratified beds of lignite or Miocene coal. On the 

 continent of Europe Miocene strata occupy immense independent 

 areas, extending from France and Spain to the Black Sea. In 

 places too numerous to name they contain beds of " brown 

 coal," as lignite is sometimes called. These coal-beds are often 

 of great thickness and solidity. In one of the pits which I 

 descended near Teplitz, in Bohemia, the coal, which lies in a true 

 basin, is 40 feet thick, and underneath it there is a bed of clay, 

 w ith rootlets, quite comparable to the underclay which is found 

 beneath almost every bed of coal in the British and other coal- 

 fields of the Carboniferous epoch. The Miocene rocks of 

 Switzerland are familiar to all geologists who have traversed 

 the country between the Jura and the Alps. Sometimes they 

 are soft and incoherent, sometimes formed of sandstones, and 

 sometimes of conglomerates, as on the Right. They chiefly 

 consist of fresh-water lacustrine strata, with some minor marine 

 interstratifications which mark the influx of the sea during 

 occasional partial submergences of portions of the area. These 

 fresh-water §trata, of great extent and thickness, contain beds 

 of lignite, and are remarkable for the relics of numerous trees 

 and other plants which have been described by Prof. Heer of 

 Zurich w'vAi his accustomed skill. The Jliocene fresh-water 

 strata of the Sewalik Hills in India are well known to most 

 students of geology, and I have already stated that they bear 

 the same relation to the more ancient Himalayan Mountains that 

 the Miocene strata of Switzerland and the North of Italy do to 

 the pre-existing range of the Alps. In fact it may be safely 

 inferred that something far more than the rudiments of our 

 present continents existed long before Miocene times, and this 

 accounts for the large areas on those continents which are fre- 

 quently occupied by Miocene fresh-water strata. With the 

 marine formations of Miocene age this address is in no way 

 concerned, nor is it essential to my argument to deal with those 

 later Tertiary phenomena, which in their upper stages so easily 

 merge into the existing state of the world. 



Glacial Phenomena. — I now come to the last special suljject 

 for discussion in this address, viz., the Recurrence of Glacial 

 Epochs, a subject still considered by many to be heretical, and 

 which was generally looked upon as an absurd crotchet when, 

 in 1855, I first described to the Geological Society boulder-beds 

 containing ice-scratched stones and erratic blocks in the Peimian 

 strata of England. The same idea I afterwards applied to some 

 of the Old Red Sandstone conglomerates, and of late years it 

 has become so familiar, that the effects of glaciers have at length 

 been noted by geologists from older Palaeozoic epochs down to 

 the present day. 



In the middle of last July I received a letter from Prof. 

 Cieikie, in which he informed me that he had discovered mam- 

 milated motifonnie surfaces of Laurentian rocks, passing under- 

 neath the Cambrian sandstones of the north-west of Scotland 

 at intervals, all the way from Cape Wrath to Loch Torridon, 

 for a distance of about 90 miles. The mammilated rocks are, 

 says Prof. Geikie, "as -well rounded off as any recent roche 

 r/wntonnJe," and " in one place these bosses are covered by a 

 huge angular breccia of this old gneiss (Laurentian) with blocks 

 sometimes 5 or 6 feet long." This breccia, where it occur-, 

 forms the base of the Cambrian strata of Sutherland, Ross, and 

 Cromarty, and while the higher strata are always well stratified, 

 where they approach the underlying Laurentian gneiss "they 

 become pebbly, passing into coarse unstratified agglomerates or 

 boulder-beds." In the Gairloch district "it is utterly unstrati- 

 fied, the angular fragments standing on end and at all angles," 

 just as they do in many modern moraine mounds wherever large 

 glaciers are found. The general subject of Palccozoic glaciers 

 has long been familiar to me, and this account of more ancient 

 glaciers of Cambrian age is peculiarly acceptable. 



Tire next sign of ice in Britain is found in the Lower Silurian 

 rocks of Wigtonshire and Ayrshire. In the year 1S65 Mr. 

 lohn Carrick Moore took me to see the Lower Silurian grapto- 

 iitic rocks at Corswall Point in Wigtonshire, in which great 

 blocks of gneiss, granite, &c., are imbedded, and in the same 

 year many similar erratic blocks were pointed out to me by Mr. 

 James Geikie in the Silurian strata of Carrick in Ayrshire. One 

 of the blocks at Corswall, as measured by myself, is nine feet in 

 length, and the rest are of all sizes, from an inch or two up to 

 several feet in diameter. There is no gneiss or granite in this 

 region nearer than those of Kirkcudbrightshire andArran, and 

 these are of later geological date than the strata amid which the 



