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GEOLOGY OF PERU-ADAMS. Accompanying this paper will be found a bibliography of tbe more important literature, and in the footnotes some additional refcr- the Pacific slope of the Andes. This is largely determined by eleva- ences are given. Nearly all of the literature of the subject hns been tion and temperature, and is indicated as one travels from town to consulted in the preparation of this reriem, but it has not been deemed town by the character of the roofs of the houses of the natives. The advisable to publish a more complete bibliograpliy, since some of the writer in drawing the line upon his published maps used this as a articles with elaborate titles have in reality little value and, hing basis for his observations arid inquiries in order to obtain reliable Pite inaccessible to the general student, can hardly hope to hold a information. place mith the more important contributions, whicll embody the Near the Gulf of Guayaquil, where the Zone of rainfau is deflected essential hths mith femer errors. to the westward from the slope of the Andes over the coastal plains arid to the Pacific Ocean, tlie division between coast and sierra VOU~~ PHYSICALAND GLI~~ATICREGIONS. be made by continuing the trend of the line into Ecuador, talfing into consideration the character of the agricuh!,ure, wlli~hvaries TBQ THREE REGIONS OS PmRU. with the temperature &pendent On elevation.but in Ecuador3'0r Peru it isthe less distinc- tion based On climate hol& fairly The dominant physical feature of Peru is the lofty range of tlle Andes ~vhichlies near the Pacific Ocean arid forms a barrier bet~een factory, since under the Equator arid in a region of rainfall the ZOnes the narrow strip of desert coast end the Mensive mooded plains of of Vegetation and agriculture do not correspond with the topographic \ disti&tion also implied. the Amazon. Accordingly, the country is commonly recognized 8s presentiW naturally defined regions which dieer in their P~YS- D~~;~~~of the coastaz region. lcal features arid climate; namely, the coast, the Sierra, arid the forest, Pr " montaiia," aS it is called in Peru. The use of these terms orig- The coastal region of Peru may be divided into plains areas arid lnated with the inhabitants, md they have to a considerable extent mountainous areas. The plains, according to tlieir geographic POS~- found their aay into scientific literature. ~h~ name L' rnonta6a " is tions in the country, may be called the '(northern," ('south central,>' 'Pt to be misleading, especially to a foreignep, it suggests moun- and L' southern.') Beiween the northern arid south central plains, and tains' " Seiva," meaning forest, nould seem to be mors approprhte* likewise between the south centralarid southern, thß CO~S~is moun- I* terms are selected which may be broadly used in considering the tainous. The northern arid south Central pl&s extend inland from South American continent one may appropriately spealc of. the ~acific the shore of the Pacific,but the southern plnins are separated from Oastal region, the Andes Mountain region, arid the Amazon plains the sea by a coast range of hills. The mountainous divisions of the region. These terms have physiographic signifiCation arid should coast are diversified by the stream valleys and their tributary dry intO Use in s~i~tificwritings. The extension of these re@~ns valleys and present a. very brolren topography. The southern On0 of maJ' be learned from the accompan~ingmap these two mountainOusareas, considered as 8 mass, riss abru~tl~ 1) from the arid presents many aspects 0f a dissected plateauarid ThethO 'PACmI'C COASTAL REGION. northernmountains area rise is in characterized a ragged, irregular b a more WaY brolren toward coast the line It ., would seem to be an Open q~e~ti~n"S to V'hether thesemountainous . lhedist%ti~n between the coast an4 the areas should be Classed with the CO~S~Or the Andes re&ion. A1ong lSOne of ~llmatearid is indicated by.differencesin aariculturaas commonlyIn made the the innerborder of the plains are the ." foothills " risink to tlle. Sierra,.. agric~lt~ralproducts arp those of the btropical arid sub- arid at corresponding distan~einland in the mountainous dlvlslOns tro~lcal climates; while those of the of the coast there is B transition Zone lmown aS the " valley heads of the temperate ZOneS The transition from On0a, such , „, found in .the coast (cabezeras de los valles)iculture where of the the valley const fioorsis impossible, become abrupt because 0f the steq declivity of the re~oni0 the other is narrow arid stony, so that the agr Andes, eit.er side into the temperature and cli- gcifi,slope of the and the mountains rise on with the exce~tionof the Part of Peru %djacenttO the GUlf 0f mate of the Sierra. 'yayaquil' the divisiOn betwe~the coast arid the - as plates Nos- '1 4$ 5. BIaarsPePI:oaueea in this report the 'PProximaie Western Bmit of genepal annualcorrespond~rainfall on . 389 388 ANNUdt REPORT SMITHSONUN INSTITUTION, 1908. GEOLOGY OF PERU-ADAMS. THE ANDES MOUNTBIN REGION. are the great inter-Andean valleys, which are &oupied by streams The distinction between the coast and the sierra has already been tributary to the Amazon and which are shown in a general way explained. [The division line between the sierra and the hazon an the hachured map, and which may be named from the rivers region would seem to be simple enough if it is based on the presence occupying them. On the Pacific slope there is one inter-Andean val- of the forest, as is implied when the word L' montana " is used. (See ley between the Cordillera Negra and Blanca lmown as the ('Valley P. 386 above.)] The tree line, however, especially in the nosthern of Huaylas " (Callejon de Huaylas). In addition sh~uldbe noted part of Pem, according to the data which the writer has obtained the Titicaca Lake basin. If one attempts to go further into the from reading, rises well up onto the flanlcs of the hdes, and indeed classification of the physiographic features, there are man7 short Covers some of the mountains which rnay be appropnately classed ranges of mountains or spurs from the main Cordillera, some of with the Andes region. It rnay also be noted that the limits of the which are named On Raimondi's map, and also high plains and table- lands (frequently called '( punas ") which are worthy of distinction. to restrict the Amazon region to the plains Jyingto the --Rn,I:<nfaZi-- ifi the Andes. 0f Fe mOuntains in Order to make the division a p~ysiograp~icone. It is possib1e to draw this line from informution now a&lable, In the accompanying The rain which falls in the Andes re@on is brought as vapor from map 0f the Cordillera of the Andes ihr the Atlantic arid most of it is precipitated in the Arnazon region or hachuring the moul~tainousarea has been done as accura~elyas on the eastern flank of the first Cordillera which it encounters. Dur- POsslble fi.om available data, bUt it dlbe remembered that Rai- mOndi's of ing the summer season the olouds rise higher arid Pass fartller to t?e which is the most detailed, is gownto be d* West, distributing their moisture on the Cordilleras and Part of lt fective3 arid t~ a ~onsiderrbleextent the bachunng it is imaguiary crosses the Continental OI? the western G0rdi1lers. It is gen-of erally believed that the *ainfall On the pacificthe s*o~e;cordilleras,the except Divdsi~mof thAn& peqdon. main which has already been disoussed, COmßS be of the bdes are the Cordilleras proper, which in the region of the Gulf of Guayaqua This is in accordance with in some detail Liter. ~omespon~~ngwith them the observations of many travelers a,nd the general theor~of the 390 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. GEOLOGY OF PERU-ADAMS. 391 inßucnce of thn trade winds. Cloiids nre not seen passing to tho Cordillera from the Pacific. The mists of the coast which drift in- The eastern chain extends on the east of Huanta, the convent of land from the Pacific form at the season when the sky in the Cm- Ocopa and Tarma, the western chain passes Castrovereyna, Huan- dillera is clear and their movements are with the land and sea breezes. cavelica, Huarochari, and Yauli, inclosing a lofty table-land. In Systematic observations of the rainfall in the Andes region have been latitude 10° 11' the two branches unite in the lrnot of Huanuco and barried on at onIy one locality, namely, Cailloma, which is situated Pasco (Cerro de Pasco). From this point northward the Andes divide into three chains. The eastern lies between the Huallaga and north of Arequipa and just to the east of the Continental Divide. Pachitea (Ucayali) riv- * From the published dattt ers, the second or cen- the writer Izas constnicted tral between the. Hual- $9- 5 % g 5 5 1837 1858 1833 1500 1901 1302 $.$Z>ZS:t? 3 3 the accompanying dia- laga and the Maranoii, d!lt:r:::n8"' z I grams (figs. 3 and 4) while the third lies be- . which show the annual tween the Maranon arid J. -------- ----------------- IlOcm --,- -----------____-___ ------- and montlily variatioils the coast. The easterri YEARS 1896-13031 of the rainfall. rang0 lowers to a ran,ae of hills, and is lost in The CorclZZZerus of tlbe 25 latitude the ------------------------ Artdes. west of Lamas. Tlze DESCRIPTIONBY EIuJJ~BOL~~~ 80cm ------------_ 1802. central, after forming the rapids and cataracts Although ~Iumboldt of the Amazon, turns to did not have Peru as an the northwest and joins object of specid stud~ the Imot of Loja in Ecuac and did not visit thß dor.

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