Sulphat of Strontian. 363 
3. Remarks on the study of Geology. 
In a recent letter to the editor, from — Minchare; 
all the rocks abiadia into four classes, or as many of them as 
pores which two classes are so different in ite 
as not to be easily mistaken. The alluvial rocks eneconih 
on the secondary, as soon as they have remained in contact 
long enough to adhere, and take the consistence of rocks, 
for the whole secondary, was at one time, alluvial, when 
they were first — th the weet ee. always 
the volcanic.” 
the memoirs of geology there tle inaccuracy in 1 
names of the rocks which should a: as strictly scientific as 
possible 5 the Wernerian nomenclature 1 is still the best under- 
Every such hint, coming from such an authority as Mr. 
Maclure than whom no man (with the single exception of 
Col. Gibbs,) has so good a right to give advice on the sub- 
ject of American geology, sen ag of attention — at 
have i its sage: geese in this‘ country: aes 
4. Sulphat F Strontian.. : se oa aoe 
Extract of ale the editor_from Prot ssor Douglass of the Military 
p essa itcaat dated Black Rak, k, (N- Y.) May Sth, 1820. 
My Dear Sir, peas! 
mineral hI had ounced - you upon a slight 
The hie of b see Vol. II. p. 241) 
