108 Iddings and Cross — Occurrence of Allanite 



town of Fomatlan (40 miles S.S.E. of Cape Corrientes, a 

 village of 800 inhabitants, belonging to the canton of Maseota 

 in our state of Jalisco, at a height of some three to five thousand 

 feet, between four and five p. M. It was a very clear day. 

 Many persons saw the aerolite, and heard the explosion it made, 

 which was very powerful. Its direction was from S.E. to 

 N.W. It left a white cloud in its track. Two or three frag- 

 ments fell, eight miles N.W. of Fomatlan, between the houses 

 of the Gargantillo farm. The latitude of Fomatlan is 19° 44' 

 1ST. and its longitude near 6° 20' W. of the city of Mexico. Its 

 elevation above the sea is about 100 feet. 



"The administrator of the Gargantillo farm, Cesareo Rodri- 

 guez, gathered two or three fragments of the meteorite a few 

 minutes after their fall, when they were still at a burning heat. 

 The largest of these weighed about two pounds. The main 

 body of the meteorite, which must have been very large, con- 

 tinued on its path to the N.W. and fell into a large lagoon four 

 or five miles distant from the farm. 



" My uncle, Mr. Joaquin Castanos, who was at that time in 

 Fomatlan, received one of the fragments from the hands of 

 Cesareo Rodriguez, and kept it for me. I made a determina- 

 tion of the specific gravity of the meteorite upon a fragment 

 weighing 28-J- grams, the result of which was 3 - 49." 



A late letter gives August, 1879, as the time of fall. 



Art. XIV. — On the widespread occurrence of allanite as an 

 accessory constituent of many rocks ; by Joseph P. Iddings 

 and Whitman Cross, of the U. S. Geological Survey. 



More than a year ago, while engaged in the microscopical 

 study of rocks from widely separated regions, the writers 

 observed in the thin sections occasional crystals or grains of a 

 highly refracting, brown mineral, which was not referable to 

 any of the more common rock-building species. The study 

 of a number of sections showed that the crystals were mon- 

 oclinic and apparently isomorphous with epidote, that is, 

 elongated in the direction of the ortho-axis with the base and 

 orthopinacoid well developed, two positive orthodomes less 

 prominently, and with terminal planes belonging apparently 

 to the unit prism. In a few instances imperfect', cleavage was 

 noticed parallel to i-1 and O, and in one case to i-\. A twin- 

 ning parallel to i-i, as in epidote, was frequently observed. 



The optical axes were found to lie in the plane of symmetry, 

 one of the bisectrices making an angle of 35° to 40° with the 

 vertical axis and 25° to 30° with the clino-axis. A strong ple- 

 ochroism, from light yellowish brown to dark chestnut brown 



