Mineralogy and Geology. 133 
smaller specimens, each of which was enveloped in a sac, an appear- 
ance which I had never before noticed in connexion with these remains. 
his sac was of an oval form, about twice the diameter of the enclosed 
Orthoceratite, enveloped its whole length, was like it pe at and had 
a longitudinal depression through its entire length. Upo seeing it, 
the idea was at once suggested that here was a solution of the question, 
never before determined, with regard to the form and texture of the 
body of the Orthoceratite. Though very widely distributed thavhigh 
various strata, yet the soft parts have been so completely destroyed by 
time and eset | that no discovery of them had been hitherto 
made, by w even a surmise could be formed of the organization 
of the meted. “a 8 a From the present discovery, we may reasonably 
suppose that they were furnished with a fleshy body, like the Sepia of 
We have received a communication 0 on Mr. Anthony’s paper, from 
Mr. James Hall of Alban y, who takes the ground that what is repre- 
sented as due to the soft parts of i Orthoceras, is a result of concre- 
tion about the fossil. He mentions and figures numerous exaniples of 
similar appearances about fossils ve various kinds, Orthocerata and 
others, which are nothing but a result of a con ae areed structure ; 
and states that such forms are rie common in the soft shales. 
The ae surface and bilobate form are common in aa New York 
specim Moreover r, it is doubted that the “soft parts” could be- 
come petitied, or retain their form sufficiently during the 08 which 
immediately follows death to give it to the enclosing material. 
7. Effe usion on n the Density of Rocks ——In the last volume, 
p- 258, some facts are given relative to the change of density in differ- 
ent siliceous minerals, in consequence of fusion and their assuming a 
vitreous state. Delesse has experimented upon this subject, and gives 
the following table cogtaining the diminution of density for the differ- 
ent rocks mentioned: (Jour: de Pharm. et de Chem., xii 68. ) 
Casaines. quartzose porphyry and eke rocks, 9 to 11 per ct. 
Syenitic granite, syen 6 ee: 
Red, brown, green ene wih or without 
quartz, and havin g a base of albite, oligo- 8.40: 10'>. 
clase, andesite 
Diorite and diorite RorPhyey Rae ole! ee 18 ee 
sy tah . - - 8 ie Ae 
Trach - - «pe te 5. ® 
fesion Dilcenic ibs col basalt - - : : ‘s 4% 
Modern — rocks and la - + EE 
8. Talus Slopes.—In the chains ns of the Vebnes and ae Leblane 
found no talus exceeding an inclination of 35°. iis slope, he ob- 
serves, is most rously, the inclination of the diagonal of a cube. 
The density of the material no effect on the slope, as 
lanches of snow and fall of rocks take the same slope. Some rough 
rocks, as trachyte and sandstone debris, may form a declivity of 37° * 
10°89°. ibrium. , 
A talus of 42° to 45°, is not one of stable equil 
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