Structure of the Amazons Valley. 361 



subsidence lias taken place since the Conquest* ; for an Inca- 

 rial road, with side- walls intended to run along the coast, 

 starts from Pacasmayo, and ends in the sea some three miles 

 south. 



The western Cordillera is doubtless Mesozoic, the Pacific 

 side being probably Jurassic, as in Southern Peru, and the 

 oriental side Cretaceous. From the slope facing Pacasmayo 

 I obtained Jurassic Cardiums and Ostreas, and an Ammonite 

 resembling^. Murchisoni. Above Balsas, near Tomependa, 

 Humboldt found and Von Buch determined Echini, Isocardias, 

 Pectens, Ostreas, and Ammonites of Cretaceous age ; and 

 similar forms were discovered by Raimondi below, within the 

 department of Ancachs. Half a day's journey west of Cha- 

 chapoyas is a highly fossiliferous limestone, abounding with 

 Ammonites and Pectens, which, according to Professor Hyatt, 

 are Liassicj". The fossils are most common along the left bank 

 of the Utcubamba, near Tingo. Some of the Ammonites are 

 a foot in diameter. Belemnites and Starfishes have also been 

 found further down the Utcubamba, near Bagua ; and at San 

 Carlos is an extensive salt deposit. The dark-brown shale 

 near the summit of Piscoguanuna, dipping strongly to the east- 

 ward, contains numerous Middle-Lias Ammonites. The rapid 

 Cachiyacu, tearing its way down from the Punta de Schalca, 

 brings along many Ammonites and Brachiopods of Cretaceous 



* I have elsewhere called attention to the singular fact that every suc- 

 cessive measurement of the Andes gives a reduced elevation, tempting 

 one to believe that either the chain is sinking- or the atmospheric pressure 

 increasing. Thus, Humboldt (1803) made the altitude of Quito 9570 

 feet ; the writer (18G7), 9520 ; Reiss and Stiibel (1870), 9350. Pichincha, 

 according to Humboldt, is 15,922 feet; according to the writer, 15,827; 

 according to Reiss and Stiibel, 15,704. In 1827 Pentland verv carefully 

 estimated the altitude of Lake Titicaca at 12,795 feet ; and Friesach, in 

 1858, determined it to be 12,030 ; but the recent railway-levellings from 

 the coast make it only 12,493. 



+ The following is an abstract of Professor Hyatt's paper presented to 

 the Boston Society of Natural History, January 20, 1875, entitled "Notice 

 of Jurassic and Cretaceous Ammonites collected in South America bv 

 Professor James Orton, with an Appendix upon the Cretaceous Ammonite's 

 of Professor Hartt's collection " : — 



" JuRASsrc Ammonites (Lias) : — Arnioceras coras, Agassiz (Amm. 

 ceras, Giebel) : under this name I have been obliged to describe several 

 badly preserved specimens, which resemble in their characteristics very 

 closely this well-marked species of the Lower Lias : he. Piscoguanuna, 

 Northern Peru. Arnioceras miserabilis?, Hyatt {Amm. rniserabilis? , 

 Quenst.) : loc. Piscoguanuna. Caloceras Ortoni, Hyatt : this new species 

 is closely allied to Amm. sironotns, Quenst., a 1 so a Liassic species : he. 

 Tinj>o, Northern Peru. Phylheeras Loscombi, Hyatt (Amm. Loscombi, 

 D'Orb.) : this is another Lias form, probably Middle Lias, from the same 

 locality. Perisphinctes anceps, Waagen : this species indicates the presence 

 of the higher divisions of the Jura, the Lower Oxford of Oppel, perhaps 



