Rejoinder of Prof. Shepard to Prof. Del Rio. 131 
’ Art. IX.—Rejoinder of Prof. Suerarp to Prof. Det Rio. 
I recret being obliged to vindicate myself farther against the 
misapprehensions of Prof. Dex Rio. It isa subject of much less 
concern, however, to find my system opposed by an individual whose 
long familiarity with mineralogy leaves no occasion for him to apply 
to analytical tables in the way of a learner, than to have its value 
called in question by that class of persons for whom it was expressly 
designed. Still I would not affect to be insensible to the good opin- 
ion of one so much my senior in the cultivation of this science, as 
-must be a pupil of Werner; though I confess some surprise at the 
grounds. on which he has seen fit to withhold his approval. 
In the few remarks I have to make, I shall pursue the order of — 
his observations. on my reply, p. 384 of the last number of this 
Journal. He asserts that I could not have chosen a worse ex- 
ample than Rutile, as a mineral for testing the comparative mer- 
its of the two systems in dispute. He objects, because he is ac- 
quainted with no Rutile “which is fine granular, or impalpable.” 
But I have no where said that Rutile occurs impalpable. My words 
were, massive in small closely connected individuals. 1 trust that 
these two conditions of mechanical composition are not confounded 
by Prof. Det Rio, since the difference is as great as that between 
snow and ice! “Nor is the objection valid because fine granular Ru- 
tile does not exist, since it is a well known variety both at Arendal 
and the southern coast of Cornwall, besides occasionally occurring 
in the New England states. But if this variety were wholly un- 
known, the employment of Rutile to illustrate the characteristics in 
question, so far as relates to crystallized and easily cleavable indi- 
viduals, would be perfectly suitable ; though my rule for referring 
minerals to the semi-crystallized class, would but seldom allow the 
broken and imperfect crystals, and large granular varieties, to be de= 
termined in this class, for I have intended for it only such as are ea- 
sily and distinctly cleavable, and such is not commonly the fact in 
_ Rutile, as any one may assure himself by attempting to cleave the 
Nigrine pebbles of Ohlapian. I must therefore be allowed still to per- 
severe in recommending the pupil to determine Rutile in a great num- 
ber of instances by a reference to the uncrystallized class, notwith- 
standing the remarks of Prof. Dex Rio respecting the impossiblity of 
distinguishing it from Ostranite, if obliged to adhere to the princi- 
