Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/104

Retrogradations along the edges of the terminal faces formed by the incidence of these faces on the sides of the prism, at an angle of 66° 38′.
Number of the modifi- cations.	Figure of the crystal	Angles formed by the meeting of the new planes with the terminal faces	Angles formed by the meeting of the new planes with those of the prism	Angles formed by the meeting of the new planes with those of the 11th modification.	Nature of the retrogradations
11th	Primitive crystal having the edges of its terminal faces of 66°, 38′ replaced by a plane	139°, 10′	107°, 28′		Retrogradation by two rows
12th		145°, 9′	101°, 29′	174°, 1′	Retrogradation by three rows

Intermediate retrogradations upon the acute angles of the terminal faces that concur in the formation of the acute solid angles of the primitive crystal
Number of the modifi- cations.	Figure of the crystal	Angles which the edges uniting the new planes forms with the terminal faces	Angles which the edges uniting the new planes forms with the edges of 92°, 30′	Angles of incidences between the new planes	Angles of incidences between the new planes anbd the terminal faces	Nature of the retrogradations
13th	Primitive crystal having its acute solid angles replaced by two planes	98°, 26′	136°, 34′	136°, 58′	110°, 20′	Retrogradation by a single row, which while it tkaes one molecule from one of the sides of the acute angles, takes two from the other
14th		81°, 59′	153°, 1′	134°, 64′	82°, 32′	Retrogradation by a single row in breadth, and two in laminæ in height which, while it takes one molecule from one of the sides of the acute angles, takes two from the other