FOSSIL REEFS: JURASSIC 437 



lowed again by non-marine sedimentation in later Middle and Upper 

 Triassic time. While the period during which reefs were forming 

 corresponds largely to that during which the Wellenkalk and 

 Muschelkalk were forming north of the Alps, it probably continued 

 to some extent into the time when the continental sedimentation be- 

 gan in the north. 



In view of this relationship of the reef to the old coast line, the 

 development of certain accessory features becomes of interest. 

 Thus the interfingering, the cross-bedding and the irregular over- 

 lapping structure characteristic of the more or less inclined beds 

 on the flanks of the reef (Uebergnssschichtnng) with their irregu- 

 lar swelling and the union and separation of layers, are confined to 

 the parts of the reefs farthest away from the old shore, i. e., the 

 southern or outer side of the reef, where it was exposed to the 

 wave destruction and where it rose steeply from the sea. The 

 lagoon side, on the other hand, is characterized by the abundance of 

 Diplopora related to the modern Cymopolia, delicate, branching 

 corallines, which abound only in the protected waters of the lagoons, 

 and do not occur on the outer side of the reef, where the stony 

 nuUipores find a congenial habitat. 



In the upper bedded strata of the Cassian formation, coarse 

 oolites are common in the eastern part of the reefs, a feature asso- 

 ciated with the closing stages of reef formation at the present day. 

 The Raibler beds overlying the reefs also are oolitic, and contain 

 many layers of calcarenytes. A remarkable feature of these dolo- 

 mite reefs is the accompanying eruptive series of augite porphyry 

 lavas, wdiich began after the reef had already assumed massive pro- 

 portions. The reef masses thus appear to have set a limit to the 

 extent of these lava flows in one direction, and they spread over the 

 submerged flanks on which the clastic sediments, formed by the 

 destruction of the reef, had accumulated. The result was the 

 formation of a remarkable limestone tuff breccia, which is com- 

 monly found at the base of these flows. 



The Jurassic Reefs of Solnhofen. In the Jurassic beds of 

 the Solnhofen district in Bavaria, famous for its lithographic stones 

 and the beautifully preserved fossils found in it, reef structures are 

 well developed and have recently been fully described by Walther 

 (91). The thin-bedded lithographic layers (calcilutytes) are found 

 to rest in shallow basins in a coarse, unstratified or rudely stratified 

 limestone with which they interfinger at the margin of the basins, 

 and which even rises above the level of the youngest of the litho- 

 graphic stones (Figs. 93-95). These coarse, unstratified limestones 

 are reefs on a large scale, composed chiefly of sponges, corals and 



