OF CONCHOLOGY. 227 



ably continues northward to Mariposa, where it is well defined. 

 Here we first met with a very interesting and new species, Helix 

 Hillebrandi, Newc, which is apparently a hirsute form, bearing 

 the same relation to H. Mormonum that sequoieola and infumata 

 do to Dupetithouarsi and Jidelis. Like the two former it inhabits 

 a drier and warmer region than its prototype, and like infumata 

 shows lower development by its angulation. (Mr. Gabb brought 

 dead specimens of Mormonum from "the head of San Joaquin 

 Valley," which is in Fresno Co., but they were probably washed 

 down the stream from a higher elevation than that of Mariposa). 

 The Hillebrandi is only known elsewhere at " Cold Springs," 

 within 25 miles north of Mariposa. The limestone ridge dis- 

 appears not far north of Mariposa, but probably some thin veins 

 of it extend to Copperopolis, which is in the same direction, and 

 where Mr. Goodyear mentions that calcite occurs, though rarely. 

 Here I found five specimens of H. tudiculata, as before mentioned. 

 The elevation is about 1000 feet, and a little farther northwest 

 the veins must disappear under the tertiary foot-hills. Among 

 these, as well as on the plains below them, there are no Helicoids 

 to be found, evidently on account of dryness, as lime is not defi- 

 cient. 



In Tuolumne Co. a new belt of limestone commences, about 

 25 miles north of Mariposa, and 10 north-east of the preceding, 

 at an elevation of about 3,000 feet. This runs north-west also, 

 and is well marked at Columbia, lat. 38°, and 2,200 feet eleva- 

 tion. Here the late Dr. Frick found the H Mormonum common, 

 alive, but only half as large as at some lower points. The lime- 

 stone ridge continues through Calaveras, Amador and El Dorado 

 counties, crossing the American river close to " Mormon Island," 

 where Dr. Newcomb discovered the species in 1856, at about 900 

 feet elevation, then disappears under the cretaceous strata. 



H. Mormonum is found along nearly its whole course, the 

 finest I have seen alive being found by Prof. Whitney in a canon 

 in Calaveras Co., near the locality of the celebrated human 

 skull, which also has a fossil specimen of the same species im- 

 bedded under its zygomatic arch, showing a similar condition of 

 things to have existed in that man's times. 



A third limestone belt commences with a similar interval, 

 north-east of the second, at Indian diggings, Amador Co., also 

 about 3000 feet elevation, and runs nearly parallel with the two 

 preceding. At White Rock, four miles east of Placerville, Mr. 

 Voy found H. Mormonum, again on the limestone, small in size, 

 and so uncommonly dark in color that it would have been con- 



