84 JUDD. — VOLCANOES. 



B. Nature of Beds Lying between Lava Currents. 

 These are of the utmost interest and value to the geologist, but 



unfortunately the ordinary mode of weathering of volcanic rocks 

 is such as greatly to obscure the iuterbedded deposits by a talus 

 of fallen fragments. The best opportunities for their study are 

 afforded by sea-cliffs, and deep ravines or river-gorges, which should 

 therefore be carefully examined. In such situations we may 

 expect to find — 



a. Burnt soils (Laterites of Lyell), usually of a brick-red 

 colour, and affording various evidences of their modes of origin. 



h. Coal or Lignite seams. These are very frequently observed. 

 Note if they rest upon an " underclay " (an old soil with roots), 

 and if they contain wood, leaves, or other plant remains, with 

 recognisable structure. 



c. Ash'beds. These are sometimes composed of such impal- 

 pable dust as to constitute a matrix in which delicate leaves, 

 shells, and even insect remains are exquisitely preserved. 



d. Stratified tuffs. Note especially the degrees and nature of 

 their stratification ; also whether they are loose or indurated. 

 They may contain shells and plants of terrestrial or marine origin. 

 Record the elevations at which the latter are found. 



e. Gravels or other deposits. Note their characters and 

 materials, and, if possible, define their mode of origin. 



C. Cones, (Craters, &c. Wherever the lavas present a fresh 

 appearance, an attempt should be made to trace them up to their 

 points of origin. 



a. If any great volcanic mountain be met with, all details 

 concerning the lava streams, fragmentary matters, and dykes of 

 which it is built up will be of great interest. Failing these, 

 however, sketches of the mountain, and of specially interesting 

 portions of it, accompanied by such rock specimens as can be 

 obtained, will be of service to geologists. 



b. Cinder-cones on the flanks of a volcano, or scattered around 

 it, should be examined and sketched. Note if they originate 

 streams of lava. 



c. The craters, both of volcanic mountains and of cinder-cones, 

 should be examined. Note if they are breached by lava streams, 

 or contain bosses of lava in their interiors, or buttress-like masses 

 adhering to their sides. 



d. Note especially the arrangement of the smaller and larger 

 cones in respect to one another. Furnish, if possible, plans lo 

 illustrate this point, or failing these, as many general outline 

 sketches as possible. 



e. In and around the craters look ^ov fumaroles, and, if possible, 

 record the nature of the gases evolved from them. Collect the 

 interesting minerals found in the crusts which are deposited 

 round the vents, and in the rocks traversed by the vapours and 

 gases. 



/. Hot springs, geysers, ^c, often occur in the vicinity of 

 active or recently extinct volcanoes. These the observer should be 



