NATURAL HISTORY OF THE DIATOMACE^E. 475 



both North and South America, is in an almost continual state of motion, and gradual 

 but constant upheaval, caused, doubtless, by the action of internal chemical changes, 

 which make themselves markedly evident in the volcanic vents found all along the 

 mountains constituting the Cascades and Sierra Nevadas of North, and the Andes of 

 South America. There have been identified at least three former lines of rise of coast, 

 and still another is seen presenting its peaks in the islands, which will, at some future 

 day, be united in such a manner as to constitute another coast range of mountains. 



If, now, we consider the bearing of these facts on the origin of the substance known 

 as guano, we find the following points worthy of note. Guano may be divided into 

 two great groups, the ammoniacal and the phosphatic ; but it is of the first mentioned, 

 only, that I desire to treat at the present time, and to which I wish to apply my de- 

 ductions. Guano is usually considered as the excrement of sea-fowl, and which has 

 accumulated during a long period of time, so long, that attempts have been made to 

 calculate its age from its thickness. Thus Humboldt, who first made this substance 

 known to the Eastern hemisphere in 1804, states, that on the Chincha islands it has a 

 depth of fifty to sixty feet, and that the accumulation of the preceding three hundred 

 years has formed only a few lines of this thickness. The facts brought forward by Mr. 

 Squier show how difficult it is to arrive at any certain knowledge on this point, and, in 

 fact, show that we have no means of ascertaining the age of the guano deposits, even 

 if we accept the theory of their origin from the source usually ascribed to them. We 

 find that guano is not confined to islands only, but occurs in large quantities on the 

 contiguous headlands ; and many ravines, extending into the interior of the country, 

 contain guano in smaller and larger quantities. Thus, the ravines of Lolo, Culata, 

 Sacramento, Animas, Morillo, Guajes, Colorado, Chucumata, and Pica are reported to 

 contain pure guano deposits, covered by a thick coating of sand. Neither is it found 

 in rainless districts only, for, as I have said, it is found on the islands off the Califor- 

 nia coast, which are by no means rainless ; and Mr. W. H. Dall informs me that it 

 occurs on the Aleutian islands, where the air is almost always saturated with moisture, 

 and heavy rains fall during a large part of the year. With regard to the upheaval of 

 such coasts along which guano occurs, it is well known, from Darwin's investigations, 

 that the whole Pacific coast of South America is in constant motion and upheaval, and 

 that on the main land near Lima, and on the adjoining island of San Lorenzo, Mr. 

 Darwin found proofs that the ancient bed of the sea had been raised to the height of 

 more than eighty feet above the water, within the human epoch, strata having been 

 discovered at that altitude containing pieces of cotton thread and plaited rush, together 

 with sea-weed and marine shells (Lyell, Principles, 1853, p. 502). 



And Darwin says, "I have convincing proofs that this part of the continent of 

 South America has been elevated near the coast at least from three hundred to five 

 hundred feet, and, in some parts, one thousand to thirteen hundred feet, since the 

 epoch of existing shells." Other proofs of this fact are not wanting, but these are 

 sufficient for me to quote at the present time. 



When the portions of guano, which are insoluble in water and acids, are examined 



