GEOLOGY. 237 



Tlie most notable North American advances of recent years in tiie 

 observation and interpretation of the resnlts of diastatic movement 

 rehite to fanltiii*;". Two <;eneti(', chisses of fanlts have h)nj;- been recog- 

 nizeu — /. e.^ normal fanlts, in which the hade (or inclination of the phme 

 of fractnre) is toward the thrown side, and reversed or overthrnst fanlts, 

 in which the hade is toward the heaved side; and in general the normal 

 fanlts have been attribnted to stresses not accompanied by hoiizontal 

 compression, and the overthrnst faults primarily to horizontal coin- 

 j)ressioM. 



A few years ago Archibald Geikie and his collaborators npon the 

 Geological Survey of Great Britain concluded that the peculiar struct- 

 ure of the Scottish Highlands is determined by overthrnst faulting 

 upon a grand scale — older strata being pushed over newer, sometimes 

 for distances amounting to miles. This conclusion Avas so novel and 

 striking, and so widely at variance from prevailing oi)inion, that despite 

 tlie ability of the geologists by whom it was enunciated and the ap[)ar- 

 ent couclusiveness of the evidence upon which it was based, numy con- 

 servative students in this country hesitate<l to accei)t it; yet within 

 the last two years there have been brought to light on this side of the 

 Atlantic almost as striking examples of overthrust faulting as those 

 of the Scottish Highlands. 



During 1880 McConnell made an extended exi)loratiou of the lto(;ky 

 IMountains among the passes follow^ed by the Canadian Pjicitic Kail- 

 road, under the direction and auspices of the Geological Survey of 

 Canada. l\\ the course of this exploration he determined the limits of 

 a renuirkable faulted region, now about 25 miles wide, though a rough 

 estimate places its original width at over 50 miles (the ditterence indi- 

 cating the amount of compression suffered), in which the faults are 

 generally of the overthrust type. The whole region is broken by a num- 

 ber of parallel, or nearly parallel, longitudinal fractures into a series of 

 oblong blocks, and these are tilted and shoved one over the other until 

 they have taken the form of a westerly dit)[)ing comi)ound monocline, 

 rising into a succession of ridges. A section through almost any of 

 these ridges, starting from the west, shows, lirst, Cretaceous shales folded 

 under older formations, ranging froui upper Carboniferous downward 

 through the Devonian and Silurian, and even to the Cambrian. The 

 overthrusts on the south fork of (Jhost Kiver rea(;h 3 or 4 miles; and 

 in these, as in some other cases, the rocks thus faulted have been sub- 

 sequently corrugated, and the original fault surface has been Hexed 

 into anticlinals and synclinals, jiarallel to those of the planes of depo- 

 sition.* 



Kecent studies in the Appalachian region by Willis and other officers 

 of the U. S. Geological Survey luive brought to light examples of over- 

 thrust faulting, ditfering only in degree from those of tlie Scottish 

 Highlands and the Canadian Eocky Mountains; and these observa- 



Kpt. D, of Anul. Kpt. Gnol. aud Nutl. Hist. C»Ui*(l» for 188<^'87, 



