1829.] 
Remarks on Cancar. 
367 
While on the subject of your Editorial notes, I may as well reply to a query 
contained in note 2d of the said page 220. Most geological writers describe green- 
stone as a primitive as well as a trapperian rock. The former is the primitive green- 
stone or trap of the AYernerians, and you may see a description of it in Jameson, 
&c. &c. Dr. Macculloch too gives a minute account of rocks “ identical with 
greenstone and basalt," which occur associated with the granites of Aberdeen- 
shire, and those he declares to lie “ varieties of the most decided granite.” From 
the above circumstance he deduces many important conclusions. This paper is 
altogether a most interesting one, and is to be found in the Journal of Sciences and 
Arts, (old series,) 1 forget the vol. but 1 quote from extracts made on reading it. 
The grunslein of the Germans include both our greenstones and hornblende rocks, 
and the same remark may be made in reference to the diabase, diorile, and amphi- 
bolite of the French. — In some late arrangements indeed, primitive greenstone is 
descrihed as a variety of hornblende rocks, “ differing from the greenstone of the 
submedial order more in geological position than in respect of composition.” — But 
in the said submedial order of these geologists is included a greenstone which occurs 
“ lying upon and interstratified with” the clay-slates, gray wake-slates and greenstone 
slates, &c. Many of these greenstones perfectly resemble the greenstones of the 
overlying trap formation, especially such of them as occur associated with the 
argillaceous schists, under which term Dr. Macculloch very properly includes both 
the clay-slates and gray wake-slates. Perhaps the terms trappean-submedia), and 
primitive or superior greenstones might, in the present state of our nomenclature, 
be sufficient to distinguish these three varieties, more especially if the term Syfnite 
be, as has lately been recommended, restricted to a rock composed of compact felspar 
and hornblende, which occurs associated with the overlying rocks. In describ- 
ing the different varieties of hornblende rock, it is difficult to convey in any one 
work, a precise idea of their nature. From pure hornblende rock down to syentic 
granite, a term adopted by Dr. Macculloch, and which 1 should be sorry to see explod- 
ed, we find them of almost every variety of structure : sometimes too, in the com- 
pound rocks, we find the hornblende replaced by actinolite, and this last also, we 
occasionally find nearlv pure, forming an actinolite schist. These with hornblende 
schist, form but varieties of one great primitive series ; and while 1 perfectly agree 
with you in thinking, that the term greenstone as applied to rocks associated with 
the granites might he changed with advantage, we must still lament the want of a 
sufficiently precise name to substitute in its place. I should be happy indeed to 
learn that this term could be confined to the overlying rocks. 
With regard to compact felspar, it. also is a primitive rock. The prino-sandstone of 
Dr. Macculloch (a rock included by Phillips in his inferior order,) is stated by Dr. 
M. to pass into comp, felspar, and lie also describes comp, felspar as an occasional 
constituent of granite and gneiss. The ensile of the French has a base of compact 
felspar, and the white stone (uieissstein of AV'erner) is a granular felspar, which is 
only a variety of the compact, while comp, felspar itself, either pure or with as- 
sociated mica and quartz, &c. is not an uncommon primitive rack. It certainly 
does occur much more abundantly as a member of the overlying trap series, both 
as a simple mountain rock, and as a constituent of the compound varieties, 
I shall conclude this most digressive epistle with one allusion to a subject of a 
very different nature, and earnestly would I call upon those of your readers, who 
take an interest in the science of oryctoiogy, to give it a share of their attention. 
It is believed by inauy' geologists, that before the existence of animals, our earth 
was covered with various plants belonging to the families of Cactus, Euphorbia, &c. 
&c. and that from the remains of these, our great coal deposits were formed. All 
who have travelled in India must have been struck with the appearance of large 
tracts which are occasionally seen covered with individuals, especially of the latter 
of these- families. On spots apparently the least likely to afford nourishment to 
plants, among bare and barren cliffs, — they seem as it were to spring from the solid 
rock, and often attain a size arid woodiness of fibre which might entitle them almost 
to the appellation of trees. That vegetables simUar to these must hare formed the 
first covering of our globe, (fitted as they are for that soilless and rocky state in 
which it must then have existed,) is a conclusion at which we almost naturally 
arrive, and an interesting comparison might be drawn between the fossil varieties 
found in Europe, and those which exist in India at the present day. With the exam- 
ple of the great Humboldt befure us, much might certainly be done to elucidate a 
subject which his discoveries have made so peculiarly interesting. 
1 am, Sir, 
lour obedient Servant* 
J, 
