TALLASITE. — CUMBERLANDITE. 79 



the porphyxitic feldspar portion, so far as the ^\Titer has observed. The structure of this 

 section is shown in Plate I. figure 6. In this the structure of the altered fissured olivine, 

 closely resembling the olivine of figure 5, is clearly shown. 



No. 1003 shows more serpentine characters than No. 1001, having less iron and 

 more of the ii-regular serpentine masses. In the section the characters are essentially 

 the same as those of No. 1001. Some talc in fine scales aggregated together was seen 

 towards the interior of the larger serpentinized olivines, and in the macroscopically visi- 

 ble serpentine masses before mentioned. The serpentme in these masses is pale-green 

 and isotropic. The serpentine replacing the olivine shows the same fibrous character 

 as No. 1001, but the structure is better marked, and the fibrous plates polarized with 

 brilliant colors. In portions of the section considerable actinolite was observed. 



Nos. 1004, 1009, 1010, and 1011 are from the side of the hill opposite to No. 

 1000, and with the preceding specimens show the gradual change from one side, on 

 which is to be found such material as No. 1000, to those masses which have suffered 

 very great alteration. Part show ochery patclies of ferruginous alteration. In general, 

 the sponge-like structure of the magnetite still remains, and besides this the interspaces 

 are variously filled with talc, serpentine, actinolite, etc. — the serpenthious material pre- 

 dominating over the others. Owing to the extreme alteration, some of these specimens 

 have developed an imperfect fissile or laminated structure, which might be mistaken for 

 beddmg planes. 



No. 1012. This was from an exposure near No. 1011, Imt separated from it by a 

 rivulet, and its connection witli the other described masses could not be shown in the 

 field. This rock is much jointed, presenting an imperfect fissile structure, and is of a 

 dark green color, witli yellowish-brown ochery spots of decomposition. On the weath- 

 ered surface, the magnetite sliows tlie irregular sponge-like structure so characteristic 

 of all these rocks. The character of the section is like that of those last described, but 

 with tlie addition to its alteration-products of considerable dolomite. I have no hesita- 

 tion in declaring my opinion, from the microscopic characters of this specimen, that this 

 outcrop belongs to the same formation as the hill itself. 



The specific gravity of the Cumberland pallasite varies according to the 

 state of the rock — whether altered or unaltered. Dr. Charles T. Jackson 

 states that it varies from 3.82 to 3.88. Mr. J. E. Wolff, Assistant in Geology 

 in Harvard College, kindly made some determinations for me. The specific 

 gravity of No. 998 was found to be 4.06 and 4.005. The former determina- 

 tion was made from a fragment containing almost no feldspar, while the 

 latter was made from one containing considerable. Again, a specific gravity 

 determination of No. 1001 gave as a result 3.50, and of No. 1003, 3.55. 



The two latter determinations were made from the more highly altered 

 portions of the rock. 



Owing to the various alterations that this Cumberland rock shows, it 



