PHYSICAL HISTORY 357 



tioii, as should be expected. Hence, while tlie sub- Williamson formations 

 maintain a marked uniformity of thickness in sections "-i'^ to "10/' they 

 are rapidly beveled away from the top downAvard to the west of section 

 "4" (Wallington) and are overlapped successively by the much attenu- 

 ated Williamson. At Rochester, where the Williamson is very thin and 

 rests directly on the lower Sodns, it contains slightly rounded flat pebbles 

 of limestone at and near its basal conduct, often standing obliquely and 

 sometimes two or three inches in diameter. There are also in the shale 

 Avorn favosite corals of similar size whose calcareous or yellowish matrix 

 indicates extraneous origin, presumably from wave destruction of neigh- 

 boring Wolcott limestone. 



The strata above the Williamson do not participate in the undulations 

 of the sub-Williamson beds, except that the Brewerton sags slightly into 

 the main (Lakeport) trough. But a general excess of upward movement 

 at the west seems to have persisted until the close of Irondequoit time, 

 maintaining clear-water (but shallow) reef^^ conditions from Niagara 

 nearly to Rochester and catching all the land wash in the sinking hinter- 

 land to the east. 



The nature and distribution of the Rochester shale show that these 

 canting movements suddenly ceased and a general submergence ensued, 

 whose terrigenous sediments appear to have come largely from a new 

 direction (farther west). Further field-work is necessary before the na- 

 ture of the sub-Rochester plane can be confidently asserted, as also the 

 relations to the upper Irondequoit and Rochester of the Lakeport lime- 

 stone. One gathers from figure 3 that the Lakeport would go more ac- 

 commodatingly below rather than above the wave-erosion plane. Pro- 

 visionally, however, the line has been drawn at the Donnelly ore. 



Another marked feature of the diagram is the great expansion already 

 described (page 337) of the basal beds at Clinton (section "11"). This 

 is now seen to be due to an earlier (pre-Martville) diastrophism, in which 

 was produced the Sauquoit synclinal. The beds involved are the Oneida 

 and supposed Maplewood. The effects of this movement farther west- 

 ward are best brought out by means of the extreme exaggeration given 

 to the thin basal members in figure 4, in which the summit of the Rey- 

 nales limestone is taken as the horizontal datum. Two movements are 

 evident in this figure : First, the post-Maple wood Alton anticline (corre- 

 sponding to the w^estern rim of the Sauquoit syncline just mentioned), 

 and, seco^id (after wave planation and deposition of the Martville- 



" This has no reference to the so-called local "reefs" of the increscent Rochester sub- 

 mergence, but to the crinoidal and other organic rubblfi of which the Irondequoit itself 

 is cora posed. 



XXVII— Bull. Gkol. Soc. Am., Vol. 20, 1917 



