Origin of Mount Etna. 389 



confined to the absence of contractions and enlargements ; this 

 uniformity pervades all the details of their structure, which is. 

 found to be invariably the same whether we observe these layers 

 in places where they are nearly horizontal, or examine them at 

 points where their inclination augments or diminishes gradually, 

 or finally trace them where they present,over a great extent of sur- 

 face, a general slope of 25° to 30°. Now, this want of relation be- 

 tween the structure of the layers and their inclination is a fact dia- 

 metrically opposed to the appearances presented by all the great 

 streams of lava, for in them the form constantly varies with the 

 intensity of the inclination. The great currents of lava owe 

 to their size itself, which permits them to spread over large sur- 

 faces, and prevents them from losing their heat for a long space 

 of time, the peculiar laws which regulate them, and which dif- 

 fer more from those that regulate the lavas occurring in stripes, 

 rounded masses, and stalactites, than the laws of a great river 

 differ from those of a small streamlet of water. 



I have endeavoured to ascertain, by a table of observations, 

 the laws of these great streams of melted matter, and have, for 

 this purpose, measured or calculated sixty-eight examples of in- 

 clinations of great currents, taken indiscriminately on the flanks 

 of Etna, in the vicinity of Naples, in Auvergne, on the banks of 

 the Rhine, in Iceland, and in the Canary Islands. I have 

 united these sixty-eight measurements in a table, and arranged 

 them in the order of magnitude, noting at the same time the chief 

 features of the current to which each of the measures refers. The 

 limits assigned to this analysis do not permit me to develop the 

 various conclusions which may be deduced from this table, whe- 

 ther considered by itself, or in comparison with other numerical 

 tables which I have also added to my memoir, viz. a table of 

 the inclinations of numerous currents of ivater ; a table of 

 the inclinations of a great many taluses qf loose matter ; and a 

 table qf the numerical amount qf a variety qf inclinations 

 to which our eyes are more or less accustomed. I shall limit 

 myself to the statement, that from this table there results tie 

 conclusion, that the structure of the rocks left by a large cur- 

 rent of lava on the surface of the ground varies according to a 

 certain law with the inclination of that surface ; tJiat their na- 

 ture is as it were a function qfthe inclination * Now, the layer^ 



VOL. XX. NO. XL. APRIL 1836. C C 



