240 Physical Observations, &fc. 



Color of the Ocean. — The color of the ocean was also attempt- 

 ed to be measured with the cyanometer, although its color is com- 

 monly regarded as green. The mode of using the instrument on 

 this occasion, was, first, by directing the eye on a small space of 

 open sea, on which the sun shone, not far distant from the ship, and 

 then to compare its color with a corresponding shade on the instru- 

 ment. Then the number of degrees corresponding thereto, was no- 

 ted, as given in the foregoing table. 



On the 10th and 11th of October, in the regions of the equator, 

 the ocean assumed a turbid or milky appearance, which is generally 

 considered by navigators, as an indication of shoals ; but this could 

 not be the case in the present instance, for, in sounding to the 

 depth of one hundred and seventy fathoms, no bottom was ob- 

 tained. 



Geology of Monte Video. 



The face of the country in the vicinity of Monte Video, is beau- 

 tifully undulating in moderate hills and valleys, and exhibits but 

 few rocks, except on the shores, where they are only of a few feet 

 in elevation. The soil is generally composed of deep beds of clay, 

 in which are often found nodules of calcareous marl. In the imme- 

 diate vicinity of the city, the rocks consist of micaceous schist and 

 quartzose sandstone. The latter, containing small particles of mi- 

 ca; sometimes passing into beds of a more compact nature, and at 

 other times, traversed by veins of quartz. At the northward of the 

 city, the rocks are almost entirely composed of this, while Rat Isl- 

 and consists of greenish sandstone, containing small spangles of au- 

 riferous pyrites. At the southeast part of the city, there are large 

 beds of talcose schist, which are traversed by veins of quartz, con- 

 taining small masses of talc. 



Kl Cerro de Monte Video, or the Mount, is elevated about four 

 hundred feet above the level of the river, and is generally covered 

 with soil and herbage. Its base consists of a coarse quartz sand- 

 stone, apparently passing into a bed of argillaceous schist, which 

 presents itself in an out cropping, near the sumpiit of the hill. The 

 aro-illaceous schist, is arranged in nearly a vertical position, but not 

 in regular stratification. At about one hundred feet above the riv- 

 er, there is a bed of marine shells of recent formation, and resem- 

 bling those found at present on the neighboring shores. 



