398 PROCEEDINGS OF THE NATIONAL MV8EUM. vol. 57. 



Since then a dozen days spent in careful observation have enabled the 

 list of species known to occur here to be considerably enlarged. Early 

 in the examination, the chloritic decomposition product was noted 

 and many specimens were collected none of which, however, was of 

 sufficient purity to encourage chemical investigation. In January 

 of this year, there was found, in the extreme southeastern corner of 

 the No. 2a quarry, a narrow fissure extending upward from the floor 

 of the quarry, on either side of which the trap for a distance of from 

 one to three feet was completely altered to a sandy friable material of 

 deep green color when wet and pale grayish-green when dry, the 

 appearance of the whole suggesting hydrothermal alteration by 

 ascending waters rather than any change dependent upon ordinary 

 surficial weathering agencies. About two-thirds of the distance up 

 the wall this fissure widened into a filled cavity from^ two to four 

 inches in width. The walls of this cavity were lined with a layer of 

 well developed prismatic quartz crystals averaging 5 mm. in length 

 over and around which was a thick deposit of a green clayey mineral, 

 the remaining space being filled with translucent calcite with a strong 

 twinning tendency. The calcite masses are impregnated by the green 

 mineral for a space of a few millimeters but are for the most part clear. 

 In the narrower portions of the cavity the calcite was absent and the 

 whole of the space between the quartz lining of the two walls was 

 occupied by the green mineral. This substance was of the appear- 

 ance and consistency of not very plastic clay. When obtained the 

 specimens were saturated with water and frozen and of a bright deep 

 green color. Upon drying, the mineral shinink remarkably, becomJng 

 completely filled with cracks and most of the specimens fell to pieces 

 spontaneously. When dry the color was pale olive green. In all 

 about 6 kilograms of this mineral were obtained, a small part of 

 which had been triturated by movement along the fissure and con- 

 tained scattered angular fragments and broken crystals of quartz 

 and calcite. Ideally pure material was available in abundance for 

 analysis and several complete analyses were made. The dried 

 mineral can be readily crushed to powder between the fingers. In 

 the closed tube it becomes brown, yields neutral water and finally 

 fuses to a black magnetic glass. It is readily soluble in hot hydro- 

 chloric and sulphui'ic acids and difficultly so in nitric acid in each case 

 with separation of flocculent silica. The specific gravity was found 

 to be 2.77. Under the microscope, this material is seen to be com- 

 posed of minute micaceous scales of uniform size and wholly irregnilar 

 outline. Basal plates extinguish between crossed nicols the mineral 

 being sensibly uniaxial and optically negative. It is transparent and 

 exhibits pleochroism in tones from pale brown to moderately deep 

 greenish brov/n. The mean index of refraction is high for a chlorite, 

 being about 1.62, about the same as that of delessite. While these 



