Skptember 7, 188:3.) 



SCIENCE. 



321 



Informal remarks on moraines and terraces. 



BY J. W. DAWSOM OF .MONTKEAL, AND J. W. 

 POWELL OF WASIIIXOTON. 



At the opening of the morning and afternoon 

 sessions of the geological section in its last day's 

 work, Dr. Dawson and Major Powell made respec- 

 tively some informal remarks of interest. Dr. 

 Dawson objected to the loose significance with which 

 the term ' moraine ' had been used, and especially 

 to the definition of it as ' detrital matter heaped up 

 by the forcible mechanical action of ice.' He pointed 

 out that such a definition would include work which 

 certainly was not performed by land glaciers. 



Dr. Dawson described the glacial deposits exposed 

 along the line of the Canadian Pacific railway, from 

 the Laurentian areas west and north of Lake Superior 

 to the Kocky Mountains, noticing the lacustrine 

 deposit of the Kcd-river valley, containing only a 

 very few, small, ice-borne stones; the second prairie 

 level covered with Laurentian drift from the north- 

 east, and with an interrupted ridge of scrub material 

 extending along the middle of it, northward from 

 Turtle mountain. lie referred to the great Missouri 

 coteau. at an elevation of 2, .500 feet, and made up 

 of local mud, and sand, with Laurentian bowlders 

 piled up against the higher prairie steppe; the drift 

 on the surface of this steppe being partly Laurentian 

 and Silurian from the east, and partly from the 

 Rocky Mountains. lie finally stated, that huge 

 Laurentian and Huronian bowlders were placed at 

 an elevation of more than 4,000 feet on the foot-hills 

 of the Kocky Mountains, mora than 700 miles from 

 their original site. He did not intend to offer any 

 explanation, as investigations into the matter were 

 still being carried on by his son; but he wished to 

 say briefly, that it appeared to him perfectly plain 

 that we could not account for such phenomena as 

 had been described, without taking into account 

 great changes of level, or, without doubt, great sub- 

 mergence and remergence. 



Major Powell called attention to the fact, that 

 wholly different agencies, each acting in its own 

 way, produced a class of geological features that 

 went under the general name of ' terraces.' We 

 have sea-beach terraces, lake-shore terraces, and 

 yet another class of terraces exceedingly common in 

 the Rocky and the Cascade motnitains. The last- 

 named class of terraces is due to a different cause 

 from the others. Some of this class in the east have 

 been relegated erroneously to the class of beach ter- 

 races: those which are said to dam the Ohio, and 

 others found in the Alleghanies, have been formed 

 by a process which can be briefly sketched. 



We have a valley. It runs irregularly between 

 bluffs and mountains. We have a force In the river 

 which simply tends down stream; it is itself ir- 

 regular, its energy depending upon its transient 

 volume and local depth. If the region is upheaved, 

 the river no longer keeps its old course. It seeks 

 the line of least resistance, and may form a new 

 flood-plain below. Then the river, for a while at 

 least, excavates laterally instead of vertically. No 



longer occupying Us old place in the valley, it grad- 

 ually cuts a new path. Hut the old terrace may 

 remain. In some places there are more than twenty 

 systems of terraces: in a locality near Pittsburgh, 

 there are fifty-three such systems. These the speaker 

 regarded as chiefly due to changes in the level of the 

 regions, — to elevations and depressions. Further 

 explanation by the speaker was cut short under the 

 five-minute rule. 



(OTHKR GEOLOair.ll P.iPKIiS.) 



The earth's orographic framework; its seis- 

 mology and geology. 



The ' continental type,' or the normal orography 

 and geology of continents. 



BY BICIIARD OWEX OF NEW HAKMONY, ISD. 



TuESE papers were read successively, as being 

 closely related. They refer to a well-known theory 

 of their author, which traces the frame-work of the 

 earth in its mountain chains. He finds such a frame- 

 work running from east to west in numerous parallel 

 ranges near the equator, and instances those of Su- 

 matra and of .South America. This he calls the 

 'strong girdle' of the earth: it is of mesozoic age, 

 terminating its heiglits in the ccuozoic age. Re- 

 motely parallel are the arctic and antarctic belts. 

 Great braces come down to meet this girdle, having 

 at least four ramifications in Asia, starting from the 

 great plateau, and in America forming the great 

 'backbone' of the continent. The five equidistant 

 continental trends of mountain chains often mark 

 paleozoic belts. But the later as well as the older 

 results tell of strong interior forces that have pro- 

 duced the mountains, and the central belt gives 

 marked evidence that an intense reaction from within 

 aided in its construction. 



The similarity of the five great continents has often 

 been the occasion of remark. They seem to have a 

 general plan of construction, that may have been con- 

 nected with their appearance as land above the ocean. 

 The similarity extends even to their present geo- 

 graphical area. If we cut cross-sections from W. S. W. 

 to E. S. E. through the geographical centre of each con- 

 tinent, we shall find in each case a seismic belt near 

 one rim of the continent, and often near both rims. 

 Thus the continent is usually basin-shaped, and cora- 

 ]iaratively low in its central area with its chief river 

 drainage, and low near the ocean borders; rising in 

 an eastern and western main range, with usually sev- 

 eral parallel subordinate ridges. These e.astern and 

 western nmuntains converge southerly, thus assum- 

 ing a somewhat irregular form, evolving usually on 

 the west some table-land. The eastern river is 

 usually paleozoic, with perhaps some mesozoic on the 

 flanks and ccnozoic on the ocean border. The west- 

 ern elevation is more commimly mesozoic in its main 

 range, and cenozoic in the flanks or subordinate ridges. 

 A section running north and south through the three 

 northern continents would successively expose Cam- 

 brian, paleozoic, mesozoic, and cenozoic cuts, which 

 would generally increase in area as we go south. 



