L170 GEOGNOSY AND GEOLOGY. 
limestone, called mountain milk. The whole dolomite series is traversed 
by extensive fissures, from which numerous caves have arisen, celebrated for 
the bones imbedded in their tertiary contents. Among these caves are 
those of Streitberg, Muggendorf, and Gailenreuth. The Solnhofen slate, 
or lithographic stone, is an important member of the Franconian Jura. 
This is a very fine-grained limestone, of a yellowish color, and contains 
many fossils in an extraordinary degree of preservation. It overlies the 
coral-rag. The Alpine Jura exhibits a very highly complicated structure, 
its masses being so much modified by abnormal rocks as to render it a 
matter of exceeding great difficulty to draw a comparison between the 
strata as they occur here and in other localities. 
Fossits or THE Jura. The fossils of the entire Jura formation exhibit 
the most interesting and varied character. Fucoids occur in great number, 
ot which, however, only one species is sufficiently well preserved to be 
noteworthy. This is Baliostichus ornatus ( pl. 38, fig. 12), an unjointed 
sea weed, with branching sporangie, and with the surface divided into 
lozenge-shaped areas, arranged in spiral rows. It occurs in great beauty in 
the Solnhofen limestone slate. Conspicuous among the Cycadee, a form 
intermediate between that of the ferns and that of the Coniferee, we have the 
Zamie, as Zamia pectiniformis ( fig. 13), in the Stonesfield slate. 
The Cycadites, or Mantelliz, are known by their almost globular stem, 
covered with lozenge-shaped leaf scars, broader than high, and disposed in 
spiral rows. Cycadites (Mantellia) megalophyllus ( fig. 14) is found in the 
limestone of the Isle of Portland. Mammillaria desnoyersi, a species of an 
ambiguous family, is represented in fig. 15. 
The coral polyps, which existed in great number in the transition rocks, 
put disappeared entirely in the entire trias period, again make their 
appearance in great profusion. ‘The Astrze, which also occurred in the 
transition, here play an important part. The most abundant species is 
Astrea helianthoides. Labophyllia semisulcata (pl. 38, fig. 16) is the 
most important representative of its family. Two genera of pedunculated 
echinoderms or Crinoidea are conspicuous: Apiocrinites and Pentacrinites. 
The former genus, possessing a very large pelvis, is exhibited only in pieces 
of the stem, and occasionally the pelvis without arms: Apiocrinites 
mespiliformis (figs. 17 and 18). An interesting species of Pentacrinites, 
P. subangularis, is shown in figs. 19 and 20. These have a pentagonal 
column, upon which arms, variously divided and subdivided, are supported 
on a very small pelvis; they are peculiar to the lias, while the Apiocrinites 
are found in the coral-rag. 
The Echini, or sea urchins, are conspicuous in the Jura formation. These 
have a more or less spherical shape, and are covered with calcareous plates 
with tubercles, upon which are jointed spines of various degrees of 
development. These may be conical or club-shaped, and may vary much 
in size. The shell is divided into regular patterns by the pores through 
which the animal extended its ambulacra or organs of motion. The large 
oral and anal apertures have different positions in the different families 
The Cidarites have the anal and oral apertures diametrically opposite to 
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