Geology and Mineralogy. 401 



Sierra, these must have been driven against the barrier until they 

 could yield no more. Thus if a pile of cloths were compressed 

 from their edges (as in Hall's famous experiment) with enormous 

 energy, they would be forced into plications so sharp that the 

 dip at any point would be nearly vertical. It seems to follow 

 that at different upheavals, some of them perhaps as yetuntraced, 

 strata to the west of the great Sierra may have been driven into 

 the nearly vertical position of the gold slates and their original 

 stratigraphical relations completely obscured. I do not consider 

 it certain, therefore, or even probable that the Carboniferous 

 slates near Pence's Ranch first assumed their present position 

 subsequently to the Knoxville period. It may be that they have 

 stood nearly as now ever since the Carboniferous of Utah was 

 raised above water, while the slates of Horsetown, of the age of 

 which nothing is known, so far as I can see, may possibly owe 

 their vertical dip to still earlier convulsions." 



9. New American Limuloid species from the Carboniferous. — 

 Prof. A. S. Packard, in a note in the American Naturalist of 

 March, 1885, mentions the discovery at Mazon Creek, Morris, 

 Illinois, of a new species of Belinurus, and one of Cychis, genera 

 hitherto unobserved on this continent ; and from the Carbonifer- 

 ous beds of Pennsylvania, a new species of Euproops. Moreover 

 the Cyclus, in its four or five pairs of limbs, " apparently of the 

 same nature as those of the larval Limuli," shows that it is really 

 a tail-less Limuloid. The species described are named Belinurus 

 Lacoei, Euproops longispina, Cyclus Americana and Bipeltis 

 diplodiscus • the last is Cyclus-like. 



10. Embryology of Limidas. — Prof. Packard closes a note on 

 this subject (Proc. Philad. Amer. Phil. Soc, Jan., 1 885) with the 

 following conclusions. The fact that the embryo of Limulus has 

 at first no abdominal appendages, and only cephalic, shows 

 divergence from the Tracheata (Arachnida, etc.) and allies it to 

 the Crustacea. The absence of a serous membrane, of an 

 amnion, of procephalic lobes, of protozonites (which occur in the ' 

 early embryo of the scorpion and spidei') show further divergence 

 from the Tracheata. The embryology is scarcely more like 

 Tracheata than the Crustacea ; it is a primitive type more related 

 to the branchiate arthropods than the tracheate and " should be 

 regarded as a generalized or composite form, which with its fossil 

 allies, the Eurypterida and Trilobita, constitute a distinct class. 



11. Town Geology: the Besson of the Philadelphia Rocks ; by 

 A^tgelo Heilprin. 134 pp. 12mo, with 7 plates, and several 

 wood-cut illustrations. — Mr. Heilprin's work is a popular illustra- 

 tion of some of the principles of geology by means of facts from 

 the vicinity of Philadelphia. The figures are good, and the ex- 

 planations of the subject simple and clear. The work will be 

 found an easy introduction to the science for the young geologist. 

 Two of the plates contain representations of Mesozoic fossils. 

 The last of the chapters is on the Drift deposits and the era of 

 ice, under the title of "Philadelphia Brick and Cobble Stone; a 

 vision of Arctic Climates." 



