152 bulletin: museum of comparative zoology. 



PA8B 



The Chagres Valley 183 



The Barbacoas Formation 183 



Keport by H. W. Turner on the Barbacoas Formation, of Barba- 

 coas, Tavernilla, and San Pablo 185 



The Mata Chin Subsection 187 



Mata Chin Formation ("Nigger Head" Bluffs) 187 



The Marine Igneous Rocks 189 



The Red Clays 191 



Topographic Bench at Mata Chin 191 



The Culebra Subsection 192 



The Culebra Basin 192 



The Culebra Clays 192 



The Culebra Mountain 193 



Section of the Culebra Mountain 193 



The Empire Limestone 195 



The Pacific Subsection 196 



The Igneous Rocks 197 



The Miraflores Beds 198 



The Panama Swamps 199 



Cerro Ancon 199 



The Panama Formation 200 



Its Relation to the Barbacoas Formation 201 



Reports of Professors Wolff and Turner 201 



The Panama Base Levelled Plain 202 



Panama Bay 203 



Continuation of the Isthmian Section across the Islands and Waters 



of Panama Bay 203 



The Geologic Formation of the Islands of Panama Bay 204 



Evidence that they are a Remnant of the Mainland 205 



Resume' of the Isthmian Section 205 



Classification of the Sedimentary Rocks 205 



Pre-Eocene Formations 206 



Fossiliferous Tertiary Beds of the Caribbean Side 206 



The Pleistocene Beds deposited synchronously on both Sides . 208 



Conclusions concerning the Igneous Rocks 209 



Cordilleras of San Bias 209 



The Older Granites 209 



Age of the Basic Igneous Rocks 209 



Late Tertiary Syenitic Intrusions 211 



Post-Oligocene Folds of the Antillean Mountain System 213 



Erosion and Base Levelling of the later Tertiary Epochs 213 



The Monkey Hill and Panama Benches 214 



The Swamp Level 214 



The Red Clays and Sub-areal Decay 215 



Part III. — The Pacific Coast from Panama to Punta Arenas, Costa 



Rica 216 



Topograph} 7 of the Interior 216 



Characteristic Elements of the Coast 216 



Sketch of Mariato Point 217 



Wave-cut Bluff and Elevated Base Levelled Plain 217 



Islands of Jicaron and Jicarita 217 



Swampy Coasts of Burica 218 



