148 ALEXANDER AGASSIZ 



winter season the sun retains a great altitude, the lati- 

 tude being 16° S., it is probable that even in winter 

 the temperature of the water remains quite high. I 

 left with the Captain of one of the steamers my deep- 

 sea thermometer and sounding line, so that he will be 

 able to carry on the observations at all months of the 

 year. 



Nearly the whole bottom of the Lake is covered by 

 a thick bed of fine black silt like an impalpable powder, 

 which of course kills all vegetation, and this in addition 

 to the high temperature of the water are the causes, 

 undoubtedly, of the small number of Fishes found in 

 the Lake and the scarcity of animal life on its bottom, 

 there being but few spots where the bottom was rocky 

 or sandy or gravelly and fitted to support animal life. 

 Of course there are extensive shoals varying from one 

 to three fathoms in depths where the Lake bottom is 

 covered with tall reeds and with weeds, but the latter 

 never reach a greater depth than seventeen fathoms, 

 eight to ten fathoms being the usual limit of the aquatic 

 plants. 



The temperature of the air is most variable at this 

 height (12,560 feet) ; the sun is extremely powerful, 

 but a passing cloud is sufficient to chill the atmosphere, 

 and in a few minutes the thermometer drops from say 

 68° in the sun to 50°, or even 45° in the shade when 

 raining, as it almost always is in the morning and even- 

 ing. At this time, the temperature remains much below 

 50° (all my figures are Fahrenheit). It will be very in- 

 teresting in the winter months to have a series of ob- 

 servations made, as during that time the sun shines 

 very brightly all day (the dry season) and from middle 

 of April to December there are but few cloudy days. 



