238 ANNUAL OF SCIENTIFIC DISCOVERY. 



point sbonld be oxncth' at the coast, then the movement of uplift 

 and ?nbsid{nR'e could go on without any change ou the shore Hne ; 

 as thi-* point departs from the siiore the extent of the alteration in 

 the position of that line would increase. Tlie way in which the 

 sea would move would, however, depend entire I}' upon the ques- 

 tion, whether the fulcrum point was to the seaward or landward 

 of the shore. Where this point lay to the seaward, then the rota- 

 tive movement would cause the land to gain on the sea; if, how- 

 ever, the pivot point be beneath the dry land, then the same 

 movement would cause the sea to advance upon the land. The 

 rapidity of the advance or retreat of the sea would depend, other 

 things being equal, upon the remoteiiess of the pivot point from the 

 shore line. 



Since we camiot suppose that the line connecting the different 

 fulcrum points can often coincide exactly with the outline of any 

 shore, it is evident that at dillerent positions this line may cor- 

 respond precisely with the course of the shore, or may pass to the 

 seaward or landwartl of that shore, so tJiat we may have the three 

 different conditions of an unchanging, an advancing, or a retreat- 

 ingsea all broughtabout b}' variations in the position of the tulcrum 

 points of the moving crust of the earth. — Abstract of Paper bij Prof. 

 N. S. Shaler, in the Proceedings of the Boston Soci. of Nat. Hist. 



PLASTICITY OF PEBBLES AND ROCKS. 



Professor W. P. Blake, at the meeting of the American Asso- 

 ciation at Salem, read an interesting pnper on the peculiar elon- 

 gated structure of tiie pebbles of the conglomerate at Purgatory, 

 near Newport, which Professor Hitchcock had maintained had 

 been elongated, compressed, and distorted b}' tension and pressure 

 after Oeing rendered plastic by an elevation of temperature. 



Professor Rogers, at the Newport meeting of the Association, 

 h:id contended that the peculiar forms of these pebbles were due 

 entirely to wave action on the oblong fragments of the original 

 metamorphic rocks. Some difference of opinion had existed among 

 geologists upon these points, but he (Prof. Blake) presented some 

 fresh evidence from a conglomerate in Arizojia Territory. This 

 conglomerate consisted of a paste of micaceous schist filled with 

 pebbles of varying size, and elongated and compressed similar to 

 those of the Ni'wport conglomerate. They presented even more 

 conclusive (evidence of having been drawn out and compressed by 

 tension and enormous pressure than even tiie Newport pebbles. 

 Eminent geologists had alleged that deep-seated rocks often be- 

 came ])lastic, and that those not much exposed to air were softer 

 than tliose on the surface. Prof. Blake then addueiMl arguments 

 an<l facts tending to substantiate this theory. The distortion of 

 hard rocks was found on a large scale in th(^ flanks of the Sierra 

 Nevada, of California. After dilating on some details bearing on 

 these i)oiiits, and referring to various hypotheses which had i)een 

 adduced ihereon, Prof. Blake said that the consideration of tlu; phe- 

 nomena led him to conclude that enormous and long-continued 



