Oct. 13, 1887] 



NATURE 



573 



Triassic, accompanied by faulting on an extensive scale; that 

 many lesser faults were produced in post-'l'riassic times, and that 

 further movements took place along the old lines of fracture. 

 He (lid not believe that the Devonian highlands were ever covered 

 by Secondary sediments, but was of opinion that the Triassic 

 rocks never extended far beyond their present boundaries, except 

 in old valleys from which they had subsequently been almost 

 entirely removed by denuding agencies. 



Observations on the Rounding of Pebbles by Alpine Rivers, 

 with a Note on their Bearing upon the Origin of Bunter Con- 

 ^omerate, by Prof. T. G. Bonney, F.R.S.— The author describes 

 the result of his observations of the rounding of pebbles in various 

 torrents and rivers in the Tyrol and Dauphine, and of the gravels 

 of the Piedmontese and Lombard plains. These lead to the 

 following conclusions, among others : (a) that pebbles are rounded 

 with comparative rapidity when the descent of the stream is 

 rapid, and they are dashed down rocky slopes by a roaring 

 torrent capable of sweeping along blocks of much greater 

 volume ; {b) that pebbles are rounded with comparative slowness 

 when the descent is gentle and the average pace of the river is 

 about adequate to push them along its bed. The rocks observed 

 were in some cases limestone and not very hard grits ; in others 

 various crystalline rocks, such as granite, gneiss, or mica-schist. 

 Hence, as the majority of the pebbles in the Bunter are of 

 harder material, and are generally better rounded than those 

 which the author observed, he concludes that it is impossible to 

 suppose them mainly derived from any tract of land which, in 

 Triassic times, can have existed in either Central or Eastern 

 England, for they must have been formed by rivers no less im- 

 portant, with courses either longer or steeper than those of 

 Central Europe. Thus these observations are very favourable 

 to the view which ascribes to them a Scotch origin, where alone 

 rocks exactly like them are known to occur. 



The Terminal Moraines of the Great Glaciers of England, by 

 Prof. H. Carvill Lewis. — The investigation here recorded is 

 based upon the important principle that every glacier at the time 

 of its greatest extension is bounded and limited by a terminal 

 moraine. The great ice-sheet which once covered Northern 

 , England was found to be composed of a number of glaciers, 

 each of which was bounded by its own lateral and terminal 

 moraines. These glaciers were studied in detail, beginning with 

 the east of England ; the North Sea glacier, the Wensley- 

 dale glacier, the Stainmoor glacier, the Aire glacier, the Irish 

 Sea glacier, and the separate Welsh glaciers were each found to 

 be distinguished by characteristic boulders, and to be defined 

 by well-marked moraines. The terminal moraine of the North 

 Sea glacier, filled with Norwegian boulders, may be seen in 

 Holderness, extending from the mouth of the Humber to Flam- 

 borough Head, and consists of a series of conical hills inclosing 

 meres. The Irish Sea glacier, the most important glacier of 

 England, came down from Scotland, and, being reinforced by 

 local ice-streams, and flowing southward until it abutted against 

 the mountains of Wales, it was divided into two tongues, one of 

 which flowed to Wellington and Shrewsbury, while the other 

 went south-west across Anglesey into the Irish Sea. This great 

 glacier and its branches are all outlined by terminal moraines, 

 described in detail. A small tongue from it, the Aire glacier, 

 was forced eastward at Skipton, and has its own distinctive 

 moraine. In the neighbourhood of Manchester the great 

 moraine of this Irish .Sea glacier may be followed through 

 Bacup, Hey, Staleybridge, Stockport, and Macclesfield, being 

 as finely developed as the moraines of Switzerland and America. 

 South of Manchester it contains flints and shell fragments, 

 brought by the glacier from the sea-bottom over which it passed. 

 At Manchester the ice was at least 1400 feet thick, being as 

 thick as the Rhone glacier. The great terminal moraine now 

 described of the united glaciers of England, is a very sinuous 

 line, 550 miles in length, extending from the mouth of the 

 Humber to the farthest extremity of Carnarvonshire, and, except 

 where it separates the Welsh glaciers from the North Sea 

 glacier, it everywhere marks the extreme limit of glaciation in 

 England, and is an important feature which might well hereafter 

 be marked on the geological map of England. 



In a separate paper, read at a subsequent meeting, the author 

 described more in detail the moraine near Manchester. 



On some Important Extra- Morainic Lakes in Central England, 

 North A'ne>'ica,and elsewhere, during the Period of Maximum 

 Glaciation, and on the 0>igin of Extra- Morainic Boulder-Clay, 

 by Prof. H. Carvill Lewis. — The lakes so characteristic of all 



glaciated regions are due to several causes. Some few are due 

 to an actual glacier scooping-out of the rock-floor, many to an 

 irregular deposition of the drift by which former watercourses 

 are obstructed, and still others to the terminal moraine or to the 

 glacier itself. These latter, known as morainic lakes, may be 

 divided into inter -morainic lakes, moraine meres, and extra- 

 morainic lakes, according to their position — back of, in, or out- 

 side of the moraine. Extra- morainic lakes, if dammed up 

 by the ice front, are temporary in character, disappearing with 

 the retreat of the glacier ; but, as they may be of enormous ex- 

 tent if the glacier is large, they may produce deposits of much 

 geological importance. Instances of such lakes occur in Switzer- 

 land, and ancient examples occur as well in Northern Germany, 

 Asia, North America, and Central England. They are to be 

 expected wherever a glacier advances against or across tnt 

 drainage of a country. Mr. Belt supposed that Northern Asia 

 was covered by a lake of this character, caused by the Polar 

 glacier obstructing the rivers flowing north. In North America, 

 where the terminal moraine has been accurately mapped for 

 thousands of miles, deposits of boulder-clay and erratics occur 

 outside of the moraine, and have been supposed to be due to an 

 older glacier in the first Glacial epoch. But the entire absence 

 of strise or of glacial erosion or moraines in this district prove 

 that a glacier was not the agent of deposition. Nor are there 

 any traces of marine life in the deposits. This extra-morainic 

 boulder-clay is narrow in Pennsylvania, where the author had 

 called it "the Fringe," but west of the Missouri it is 70 miles 

 wide ; and in British America, between the great moraine called 

 the " Missouri Coteau " and the Rocky Mountains, it is 450 miles 

 wide and over 1000 miles long. It only occurs where rivers had 

 flowed towards the glacier, and is explained as the deposit of 

 great temporary fresh-water lakes dammed up by the ice front, 

 the erratics having been dropped by icebergs. Similar deposits 

 occur in England outside of the terminal moraine, and have been 

 the subject of much discussion ; being held by some to be a proof 

 of marine submergence, by others to be the ground-moraine of a 

 glacier. The "great chalky boulder-clay " is the best known of 

 these deposits. There are serious objections to the two theories 

 heretofore advanced to explain this, whilst the hypothesis of 

 extra-morainic fresh-water lakes, dammed up by the glaciers, is 

 sustained by all observed facts. The most important of these 

 lakes was one caused by the obstruction of the mouth of the 

 Humber by the North Sea glacier, whose terminal moraine 

 crosses that river at its mouth. This large lake reached up to the 

 400-feet contour line, and extended southward nearly to London, 

 and westward in finger-like projections into the many valleys of 

 the Pennine Chain. It deposited the "great chalky boulder-clay," 

 and erratics were floated in all directions by icebei^s. The 

 conclusion that the glacial phenomena of England are due neither 

 to a universal ice-cap nor to a marine submergence, but to a 

 number of glaciers bordered by temporary fresh-water lakes, is 

 in accordance with all the observations of the author in England 

 and elsewhere. 



On the Extension of the Scandinavian Ice to Eastern Eng- 

 land in the Glacial Period, by Prof. Otto Torell. — The author 

 described the glacial deposits of Eastern England, particularly 

 those of Holderness and Cromer, the latter having been ex- 

 amined by him on several occasions during the last twenty years. 

 Applying his experience gained during winters spent within the 

 Arctic Circle, the author showed that the boulder-clay of Holder- 

 ness and Cromer is a true ground moraine formed near the 

 southerly limit of the Scandinavian ice-sheet. The Cromer 

 tills were formed by an extension of the Baltic ice; '-wedish 

 boulders brought by this ice can be traced across the German 

 plain, and are found at Cromer. The till of Holderness was 

 formed by an extension of the Skagerack, as is proved by cha- 

 racteristic Norwegian boulders. The Baltic ice retreated fifst, 

 and the Skagerack ice, still moving onward, ploughed into and 

 contorted the Cromer till. The distribution of the boulder is 

 described in detail, as also is the succession of the beds as 

 worked out by Mr. Clement Reid, whose facts and conclusions 

 fit well with the opinions advanced by the author, 



A Comparative Study of the Till or Louver Boulder- Clay in 

 several of the Glaciated Countries of Europe — Britain, Scandi- 

 navia, Germany, Switzerland, and the Pyrenees, by Hugh 

 Miller. — The sections of foreign till examined by the author 

 occur chiefly in the neighbourhood of the Trondhjem Fjord in 

 Norway, at Berlin and Leipzig in Germany, near the Lake of 

 Geneva in Switzerland, and in the valleys of the Pyrenees 



