1883.] and the region farther East. 1015 
bottom of a well forty-five to forty-seven feet deep, at Walter's 
station on the Southern Pacific railroad, the level of the Colorado 
desert at that point being 195.54 feet below that of the ocean. 
The specimen of earth was collected by Professor Davidson, 
who kindly submitted it for my investigation. Recently on his 
return from the Transit of Venus Observation station in New 
Mexico, he made a further examination in the desert, at Indio, a 
station on the same line of railroad, 109 miles north-westerly from 
Yuma (on the Colorado river), and thirteen miles this side, £ e., 
northerly from Walter’s,) where the previous collection was made. 
This new material is from the surface, at a point where the line 
of the road is twenty-seven feet below the level of the sea at low 
water. 
The soil is of the same general character as that from the well, 
an exceedingly fine sediment, friable and readily separating in 
water. The Indio sample contains numerous micaceous parti- 
cles, in this respect differing from the specimen of earth from 
Walter's station. 
The molluscan forms include fragments of the valves of the 
common fresh-water mussel of the region, Anodonta californien- 
sis, also the gasteropods, Amnicola longingua, Tryonia protea (two 
Fic. 1.— Tryonia protea. 
varieties only, one smooth the other finely cancellated), also a 
lection of between eighty and ninety of the pond-snails, 
Physa, including perfect and imperfect specimens. 
is portion of the collection is. of special interest, as it fur- 
nishes a most satisfactory, because continuous, varietal chain con- 
necting certain forms heretofore generally regarded as species, of 
which I have, on various occasions, expressed the opinion as be- 
! These places are in San Diego county, along the western flank and nearly at the 
base of the San Bernardino mountains, which traverses the region diagonally in a 
north-westerly and south-easterly direction, from the northerly boundary of the 
State nearly to its southerly line, following the axis of the range, a length of about 
150 miles, 
