57 
^tein ) is composed of two distinct rocks ; one, 
extremely compact and qnartzose, with a small 
portion of cement, and scarcely any fissures of 
stratification, lies on a schistose gritstone (sand- 
steinschiefer) ^ with a fine grain, and divided 
into an infinite number of small strata, ex- 
tremely thin, and almost horizontal. It is pro- 
bable^ that the compact and qnartzose stratum, 
when the crevice was formed, resisted the shock 
which rent these mountains ; and that it is the 
continuity of this stratum, which serves as a 
bridge to cross from one side of this valley to the 
other. This natural arch is fourteen metres and a 
half in length, and twelve metres seven decime- 
tres in breadth : its thickness in the centre is two 
metres four decimetres. Experiments carefully 
made on the fall of bodies, and with a chro- 
nometer by Berthoud, gave us ninety-seven 
metres seven decimetres for the height of the 
upper bridge above the level of the waters of the 
torrent. A well informed person, who has an 
agreeable country residence in the beautiful 
valley of Fusagasaga, Don Jorge Lozano, had 
already measured this height with a line, and 
found it to be one hundred and ttvelve varas 
(93* 4“) ; the mean depth of the torrent appears 
to be about rix metres. The Indians of Pandi 
have formed, for the safety of travellers, who, 
however, seldom visit this desert country, a 
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