October 21, 1892.] 



SCIENCE. 



231 



and formed more numerous convolutions and fissures in conse- 

 quence, but the pharynx may not be changed from the original 

 inclination. 



5. The softer brain is likely to undergo more rapid changes than 

 the harder skull, either in the evolution of species or the indi- 

 vidual, and the mere cranial conformation may or may not, 

 therefore, be an index to brain area and intelligence, and what- 

 ever changes may occur in the skull due to brain increase have 

 reference more to enabling the brain to find room in the cranium, 

 so that a higher forehead may render the more erect basi-occipital 

 unnecessary, or vice versa, and normal or abnormal growth of 

 brain may raise both osseous portions. 



Some mongrel dogs may inherit a larger brain from one parent 

 and smaller brain-case from another, which would account for the 

 deep indentations in their skulls, the pressure causing them some- 

 times to suffer from epilepsy and other brain derangements; this 

 disparity is not likely to be so great in the offspring of better- 

 mated species. 



6. Many other matters could be considered, such as centres of 

 ossification and cartilaginous persistence between such parts as 

 the basilar process and sphenoid, enabling adjustment of the 

 pharynx to the changed medulla angle. 



70 State Street, Chicago. 



INDICATIONS OF A RAINY PERIOD IN SOUTHERN PERU. 



BY A. B. DOUGLASS.' * 



It is sufficiently easy to assert that at some remote period this 

 country had abundance of water; but very few writers have 

 taken the trouble to point out the actual indications to that ef- 

 fect. 



There are two causes which operate to make this climate dry. 

 The first is found in the south-east trade- winds being stopped by 

 the high mountain ranges in the interior to the east of us. The 

 second consists in the fact that the winds which do reach our 

 sea-coast come from the colder regions to the south, and conse- 

 quently will take up moisture and not deposit it. Therefore, a 

 change from a wet to a dry climate was probably caused by a 

 considerable increase in the average elevation of the Andes. If 

 such was the case it must have occurred at some very remote 

 period. 



Before entering fully upon the subject, it is safe to remind 

 one's self that a small amount of water acting through a great 

 length of time can accomplish almost as much wearing as a great 

 amount in a short time. Therefore, the numerous large and 

 deep ravines in this region do not necessarily indicate a great 

 quantity of water at some past epoch. 



The purpose of this paper, then, is to point out some particu- 

 lars which indicate that at some geological epoch there was 

 abundance of water in this region. Unmistakable evidence has 

 been found in two places : on Charchani and on the Pampa of 

 La Joya. 



A trip to the observatory meteorological station on Charchani, 

 at an altitude of 16,650 feet, reveals many interesting facts. The 

 green valley of Arequipa seems to be alluvial flats of river and 

 perhaps lake deposits ; the pink-colored pampa of Uchumayo is 

 evidently the original volcanic tufa; while the dark-brown 

 pampa, stretching out some ten miles from the mountain and 

 containing a very thin vegetation, is an enormous " wash " from 

 the mountain itself. In this is shown a water action on a scale 

 surpassing anything that can be found about the city itself. If 

 Charchani is a remnant of an ancient crater-ring, as seems not 

 improbable, then a portion half as large as the present mountain 

 has been washed down into the valley. 



But there is a still more noticeable feature on the mountain 

 itself. At an altitude of about 14,500 feet, on the ridge west of 

 the great central ravine, the road passes for perhaps half a mile 

 through an area of bowlders worn by water action into all sorts of 

 curious and fantastic shapes. The rest of the ridge to its top is a 

 regular glacial moraine of gravel and bowlders. On leaving this 



' First assistant at the Boydun station of the Harvard College Observatory, 

 Arequipa, Peru. 



ridge and reaching the final slope to the summit, a little below 

 snow line, one finds every ledge of rock smoothed and polished 

 on the surface, with long shallow scratches pointing down the 

 mountain — proofs of glacial action. These striated ledges are 

 especially noticeable at and just below the meteorological station. 

 Therefore, at some period this pocket where our station is, be- 

 tween the main summit and the broken ridges to the east, was 

 filled with ice to a depth of a thousand feet or more. This 

 glacier slowly moved downward, completely filling the valley 

 and at some point separating into two streams, one of which 

 filled the great central ravine down to the spring, Canchero, and 

 the other turned more to the west, going down probably to the 

 same altitude of 13,200 feet. 



Now the significance of an enormous glacier on Charchani is 

 this: ravines and river valleys can be made by a small amount of 

 water acting through a long period, but glaciers cannot; the 

 water, or snow, must be all there at once. Moreover, the greater 

 the supply of snow for a glacier the farther down the mountain it 

 will come. Now, the temperature of this spring at noon of April 

 13, this year, was 45.5'^ F., and it will be shown later that 

 the land had a less elevation in the rainy period than at pres- 

 ent. The climate could not, therefore, have been colder. As 

 this glacier came down to an altitude where the mean annual 

 temperature was considerably above freezing, as shown by the 

 present temperature of the spring, the snow supply must have 

 been not merely moderate but quite abundant. 



If we had rain enough at the present day to make these dry 

 pampas the gardens they might be, this glacier would be seen on 

 Charchani. 



The evidence to be found on the Pampa of La Joya is equally 

 conclusive but not equally striking. Not far below Vitor is a 

 large ridge of volcanic mud to the west of the track. This ridge 

 runs about north-east and south-west, and is bounded along its 

 south east side by an open cliff where the bank has been caved 

 away by a river flowing against it. Stretching away from this 

 bank is the old river-bed, very broad and shallow. At a higher 

 level, to the east of the track, the river-bed contracts into a nar- 

 row and deep channel. A surface river on the Pampa of La Joya 

 would necessitate vastly more abundant rains than at the present 

 day. There must have been a supply greatly in excess of the loss 

 by evaporation or sinkage into the earth. 



There are other facts also which bear on this question. Lake 

 Titicaca once covered many times its present area. Innumerable 

 shell-fish lived in its waters, whose remains are now found as fos- 

 sils at Chililaya, Huancane, and other places, many feet above 

 the present lake-level. The signs of this increased size are still 

 so evident and the fossils are so much like the living species of 

 shell-fish, that, geologically speaking, the rainy period which 

 caused this increase and at a lower altitude supported a tropical 

 vegetation was recent ; historically, of course, its antiquity was 

 immense. The palaces and houses on the island of Titicaca were 

 built with the lake at practically its present level, and Tiahuanaco 

 is not more than 150 feet above it. Coal deposits are found on 

 the island of Titicaca and at Sumbay, but the tropical vegetation 

 which formed them must be placed in a past so remote that the 

 enlargement of Lake Titicaca and the glaciers on Charchani are. 

 but as yesterday. 



In the beginning of this article I referred to the fact that an 

 increase in the elevation of the mountains to the east of us may 

 have caused the climate to become dry. That such an increase 

 has occurred in recent geological times can scarcely be doubted. 

 From above Tambo station down to the present sea-level traces of 

 surf-action may be found. That means that the coast has been 

 gradually rising out of the sea to the extent of 1,100 feet in recent 

 geologic times. Whether it did it with perfect regularity, by oc- 

 casional periods of rapid rising, or by sudden elevations, a thor- 

 ough examination of the region would show. At MoUendo it is 

 evident that the coast has not risen more than two or three feet 

 in the last hundred years, if it has risen at all, and the fact that 

 guano has been accumulating on the islands along the coast for 

 many thousand years indicates that for a long period the coast 

 has iseen practically stationary. Nevertheless, there can be no 

 doubt that the last change in the coast-level was a rise of 1,100 



