L l THE I! 1 \ 1 1 IT A< i E S A N I >ST< » N ES. 



The three ravines above specified are veritable canyons with vertical 

 rock walls, 100 to 200 feet high, and many beautiful cascades. Besides these 

 there are many others but little less extensive, in which there may be found 

 good exposures of every horizon of the Portage group, and which have at 

 their mouths alluvial cones composed of the debris brought down by the 

 streams flowing through them. 



The more important named in order from the lake southward, are the 

 Snyder, Hartman, Biehl, Yaw, Pottle, Dunton, Lincoln and Hoecker gullies 

 on the west side, in which the lower and middle Portage beds are exposed, 

 and the Caulkins, Tyler and Reservoir or Olney gullies in the upper Portage 

 and lower Chemung. Although no single exposure gives a continuous section 

 from undoubted Genesee to undoubted Chemung rocks, the outcrops are so 

 numerous that, as the strata persistently maintain their individual character, 

 which can usually be easily recognized by the careful observer, it is not difficult 

 to join the sections with comparative accuracy. 



This report and the diagram accompanying it are the result of examina- 

 tions and measurements made at all of the best exposures in the valley. 



The contact with the Genesee slate at the base of the Portage 

 group, is not distinctly marked, and any dividing line established between 

 these tw r o divisions must necessarily be, in this locality, a somewhat arbi- 

 trary one. 



At the head of Canandaigua lake, near the Woodville hotel, there is an 

 exposure that embraces fifty to sixty feet of typical upper Genesee slate, soft, 

 dark blue-grey, in which Lunulicardium, fragile and other characteristic 

 fossils are abundant. 



By the side of the road leading southward toward the village of Naples, 

 the upper layers of the same bed are exposed for a quarter of a mile, to the 

 mouth of the Snyder gully. In this ravine the dark slaty shales are overlaid 

 by about fifteen feet of soft, clayey, olive shales that contain a few r fossils 

 common to the Portage group, but L. fragile is still the most abundant form. 

 These beds were termed by Clarke, "transition shales," and may properly be so 

 considered, as there is no recurrence of the Genesee slates, and L. fragili is 

 very rarely seen above them. Next above occur fifteen feet of dark slaty and 

 lighter sandy shales, in which are intercalated a few thin flags, in which the 

 proportion of dark shale increases toward the top, where the lighter layers 

 disappear and a bed of densely black, bituminous fissile shale about fifteen feet 

 thick is found, overlaid by fifteen feet of black and grey shale of the same 

 character as those below the bituminous layer. Plant remains are common 



