▁into ▁the ▁sea ▁with ▁a ▁great ▁ro aring ▁noise , ▁due ▁princip ally ▁to ▁the ▁action ▁of ▁the ▁t ides ." ▁ ▁The ▁map ▁of ▁Y ale ▁Gla cier ▁by ▁G ann ett , ▁the ▁description ▁by ▁Gilbert , ▁and ▁the ▁photograph s ▁by ▁other ▁members ▁of ▁the ▁Harr iman ▁Ex ped ition ▁in ▁ 1 8 9 9 ▁show ▁clearly ▁that ▁in ▁all ▁major ▁features ▁of ▁position ▁Y ale ▁Gla cier ▁had ▁at ▁that ▁time ▁assumed ▁the ▁general ▁conditions ▁which ▁pre va iled ▁in ▁ 1 9 1 0 . ▁The ▁rock ▁led ges ▁beneath ▁the ▁center ▁of ▁the ▁gla cier ▁are ▁seen ▁in ▁the ▁photograph s , ▁and ▁Gilbert ▁indicates ▁that ▁there ▁were ▁bar ren ▁zones ▁at ▁the ▁marg ins . ▁He ▁explains ▁the ▁dirty ▁ice ▁near ▁the ▁north western ▁side ▁of ▁the ▁gla cier ▁as ▁follows : ▁" A ▁black ening , ▁west ▁of ▁the ▁middle , ▁by ▁gla cial ▁dr ift ▁suggests ▁that ▁a ▁rock ▁kn ob ▁may ▁lie ▁near ▁the ▁surface , ▁ready ▁to ▁develop ▁into ▁a ▁nun ata k ▁or ▁island ▁if ▁the ▁gla cier ▁shall ▁dimin ish ." ▁The ▁photograph s ▁and ▁descri ptions ▁by ▁Grant ▁in ▁ 1 9 0 5 ▁and ▁ 1 9 0 9 , ▁and ▁the ▁map ▁by ▁H igg ins ▁in ▁the ▁latter ▁year ▁show ▁that ▁Y ale ▁Gla cier ▁maintained ▁essentially ▁the ▁same ▁conditions ▁during ▁the ▁de cade ▁following ▁ 1 8 9 9 . ▁The ▁narrow ness ▁of ▁the ▁bar ren ▁zones ▁in ▁ 1 9 0 9