S. L. Penjield—Descloizite from Mexico. 361 
4. The lower or valley ice-stream was most rapid when the 
general glacier was of maximum thickness. 
- The glacial flow probably ceased when the melting was 
half completed, except in the mountain regions and some special 
localities elsewhere of limited extent; in which case, the disap- 
pearance of the general glacier did not end in leaving one or 
sa long local glaciers in the lower half of the Connecticut 
valley. 
y 
6. Both the upper and lower ice-streams transported drift- 
material. The material from the upper that sunk into the 
lower stream was carried by it south-southwestward and depos- 
ited with the drift of the latter, and often against the eastward 
slopes of obstructing ridges. 
¢. The lower ice-stream lost its own direction of flow on 
valley ice near and over the Sound, causing intersecting cre- 
vasses, the high local till-deposit of Round Hill was produced. 
Art. XL.—On a variety of Descloizite from Mexico ; b 
MUEL L. PENFIELD. 
DuRING the spring of 1883 Professor Wolcott Gibbs of Cam- 
bridge sent some specimens of a vanadium mineral to Professor 
George J. Brush for identification. The specimens seemed to 
be fragments of a coating from one-eighth to three-eighths of an 
Inch in thickness, composed of groups of prismatic crystals 
arranged somewhat like the common crystallizations of prehnite 
orcalamine. On the top surface of one specimen minute crystal 
faces were visible, very irregularly grouped together and curved, 
ut in the other cases it simply appeared rough and somewhat 
weathered. The structure on the cross fracture was columnar- 
fibrous, sometimes radiated ; it showed at all times a fresh and 
homogeneous interior of a dark brown color and resinous luster 
very:much resembling some varieties of sphalerite. Cleavage 
distinct, parallel to the columnar structure. Hardness 3°; 
Specific gravity 6200-6205. 
Before the blowpipe it gave reactions for vanadium, arsenic, 
ead, copper and zinc. Heated in the closed tube it fused very 
readily, boiled up violently, and gave off water which reacted 
neutral to test pa 
paper. : 
€ specimens were said to be from near Zacatecas, Mexico, 
