33i 
a Theory of the Earth . 
their form, the nature of their sides, their strata, and the 
concretions adhering to them, such as sulphur, salt, &c. 
22. A. To observe the fumaroles , or jets of smoke, 
often acid, which arise ; their temperature, their nature, 
and their effects on the lava with which they come in 
contact. 
23. To examine the fissures ; whether they contain 
metallic or stony crystallisations, which may be consi- 
dered as sublimed, and formed by the crystallisation of 
substances reduced to the state of smoke or vapour. 
24. The nature of the streams of cooled lava ; their 
extent and thickness. 
25. Whether it be true that, in general, they are po- 
rous both at the upper and lower surfaces of the strata, 
and compact in the interior part. 
26. To study the nature of the different currents placed 
above each other, in order to ascertain the difference that 
may have taken place in the focus of the volcano, and 
even in the source of its lava. 
27- To examine, in general, in the lava, the nature of 
the earth and stones of which it has been formed. 
27. A. To study the origin of the crystals found en- 
closed in the lava, as the white garnets or leucites in that 
of Vesuvius, in order to ascertain whether these crystals 
have been formed in the lava since the time of its fusion, 
or whether they pre-existed in the stones from which the 
lava was produced. 
28. The nature and progress of the decomposition of 
the different kinds of lava, either by volcanic acids or 
meteors. 
28. A. Whether there are any which have actually 
been in fusion, and yet have preserved all the external 
characters which the stone had before it was subjected 
to the action of the subterranean fires. 
