and Poleanic Substances. 237 
tions of the rocks of that country, and could scarce distin- 
guish them from those collected round Ripler.” 
Psuedo Lavas. The one described by Mr. Finch, in the 
neighbourhood of Bradley in Staffordshire, halfway between 
Wednesbury and Bilson, Ann. Phil. May, 1818, p. 342, 
will suffice as anexample. It is about 14 miles in length 
by a mile in breadth. It furnishes 1 crystallized sulphur, 
2. mineral tar at the cropping out of a thin bed of coal, 3. 
rotten coal, 4, sulphat of alumina, 5. muriat and sulphat of 
ammonia, 6. sulphat of zinc, 7. sulphat of lime, 8. porcelain 
Jasper from 5 to 40 feet thick, where the clay has been in- 
durated by the burning of the coal underneath, 9. newest 
fleetz trap basalt, or ia Rag: like the Rowley Rag 
between Dudley and Oldbury, (described by Kirwan, and 
operated on by Gregory ss where the village of Rowley 
in Staffordshire now stands. I[t encloses crystals of horn - 
blende; breaks into polygonal forms, and decomposes into 
spheroidal masses. 
To account for the cause of volcanic action ? 
I consider it established, that the chief seat of volcanic 
agency is under the old Granite ; in cavities that communi- 
eate very extensively but not universally, under the crust of 
the earth; for otherwise the phenomena of earthquakes, 
sapacente as they occasionally are, would not be so often 
ocal. re 
To feed these fires there must be corsbustible matter and 
oxygen: whence are they supplied ? 
he theories on this subject are i 
Ist. The decomposition of water by the decomposition 
of sulphuret of iron. 
The objection is, that there is no evidence of sufficient 
quantity of this substance to produce. the prodigious and 
Matter, He ats3 
The objections are, that voleanoes probably existed be- 
fore coal and bitumen : for nothing but the violent action of 
volcanoes, producing powerful and destructive currents, 
could have worn down the primitive, and produced the 
Vor... TV......No. 2. a 
