ILLUSTRATIONS. 
Page. 
Plate I. Map showing location of Monterey district 13 
II. Panoramic view of mountains of the Monterey district 16 
III. Geologic and topographic map of the Monterey district 20 
IV. Crumpling of sandstone at the east end of the tunnel through Jacks 
Mountain on the Gettysburg Railroad 22 
V. Sections through the Monterey district 24 
VI. Junction of felsite and sandstone on the old Tapeworm Railroad 28 
VII. Flow structure in aporhyolite, Monterey district 42 
VIII. Flow structure in aporhyolite. Raccoon Creek 44 
IX. Spherulitic aporhyolite, Monterey district 46 
X. Aporhyolite with spherulites in layers 48 
XI. Lithophysa>, Raccoon Creek 54 
XII. Flow hreccia 62 
XIII. Acid hreccia, Raccoon Creek 64 
XIV. Sericite-schist, Gettyshurg Railroad 66 
XV. Thin sections : a, quartzite ; b, feldspar crystal 96 
XVI. Thin sections: a, perthitic structure in feldspar; &, stretched feld- 
spar crystal 98 
XVII. Thin sections: a, quartz-albite mosaic filling crack in feldspar crys- 
tal ; b, micropoikilitic structure 100 
XVIII. Thin sections : a, flow structure in an aporhyolite - x b, chain spherulites 
in an aporhyolite 102 
XIX. Thin sections: a, b, augite-porphyrite in ordinary and in polarized 
light 104 
XX. Thiu sections : a, b, perlitic parting in an aporhyolite in ordinary 
and in polarized light 106 
XXI. Thin sections: a, perlitic parting in an aporhyolite; b, axiolites in 
an aporhyolite 108 
XXII. Thin sections : a, b, altered and unaltered spherulites in aporhyolites- 110 
XXIII. Thin sections: a, altered spherulites in ordinary and in polarized 
light ; b, chain spherulites with phenocryst 112 
XXIV. Thin sections : a, b, rhyolitic structures in aporhyolites 114 
XXV. Thin sections : a, rhyolitic structure in an aporhyolite ; b, piedmont- 
ite 116 
XXVI. Thin sections : a, b, amygdaloidal aporhyolites 118 
XXVII. Thin sections: a, b, tridymite spherulites in an aporhyolite 120 
XXVIII. Thin sections : a, augite-porphyrite ; b, melaphyre 122 
9 
