10 



ILLUSTRATIONS. 



Plate. 



Jurassic cycads from Wyoming xlvi-lxiii 



Sketch map stiowing fossil localities of the Shasta formation of California . _ _ _ . lxiv 



Ferns from the Shasta formation of California and Oregon lxv-lxvi 



Cycads from the Shasta formation of California and Oregon — lxvii 



Cycads and conifers from the Shasta formation of California and Oregon , lxviii 



Conifers and dicotyledons from the Shasta formation of California and Oregon lxix 



Cycadean trunk from the Shasta formation of California lxx 



Ferns from the Kootanie formation of Montana l.\xi 



Equiseta and cycads from the Kootanie formation of Montana Lxxii 



Cycads and conifers from the Kootanie formation of Montana and the Lakota formation 



of South Dakota lxxiii 



Exposure of the Potomac formation on Ontario avenue, Washington, D. C lxxiv 



Exposure of the Potomac formation on Kansas avenue, Washington, D. C lx.xv 



Exposure of the Potomac formation on Sixteenth street, ATashington, D. C lxxvi 



Exposures of the Potomac formation at Terra Cotta, D. C Lxxvit 



Exposures of the Potomac formation at Freestone, Virginia lxxviii 



Exposures of the Potomac formation on Back Lick Run, Virginia lxxix 



Map of the Potomac terrane in Maryland, the District of Columbia, and adjacent parts of 



Virginia lxxx 



Cycad trunk and silicified wood from the Potomac of Maryland _ lx.xxi 



Trunks of cycads early discovered in the Potomac of Maryland lxxxii-lxxxti 



Group of cycads in the Museum of the Woman's College of Baltimore lxxxvii 



View of the Link Gulch with the Link cycad in place lxxxviii 



Group of cycads in the Museum of the Woman's College of Baltimore Lxxxix 



Cycadeoidea marylandica xc-.xcii 



Cycadeoidea Tysoniana — xciii 



Cycadeoidea McGeeana - - xciv 



Cycadeoidea Fontaineana xcv-xcviii 



Cycadeoidea Goucheriana — xcix 



Cycadeoidea Uhleri c 



Cycadeoidea Bibbinsi ci-civ 



Cycadeoidea Fisherse cv 



Cycadeoidea Clarkiana - cvi 



Fossil plants from the Potomac of Virginia, the District of Columbia, and Maryland ovii-cxix 



