108 Mr Oscar Fraas' Observations on the Effects 



more destitute is the lias of the sandstone formations. Thus 

 also were formed similar strata of the lower " black Jurassic"' 

 formation, which appears as an alternation of limestone 

 and sandstone in proximity to the shore ; and far from the 

 shore, in the depths of the sea, as a pure calcareous deposit. 

 Normandy is a normal type for pure pelagic precipitations ; 

 formations far from the shore in the open sea. Here sand- 

 stone is not at all known in the Jurassic series. The thickness 

 of the strata is quite insignificant, because accumulations are 

 not possible in the open sea. In this lias, saurians, fish-teeth, 

 and breccia (which prove the proximity of a shore), are either 

 not found at all, or are exceedingly rare. At Fontaine 

 Etoupefour (Depart. Calvados), the whole lias is from 6' to 

 8' thick, but even in this thickness all the divisions of the 

 lias are represented in miniature ; a proof that the thickness 

 also of the strata and not their materials only, depend upon 

 the proximity or distance of the shore. 



2. The depth or shallowness of the sea exercises an influ- 

 ence upon the conditions of its inhabitants, and consequently 

 upon the species of the imbedded organic remains. We seek 

 in vain in the Swabian lias for corals, which are especially 

 evidence of shallow seas ; Calvados is very rich in them. In 

 Burgundy, the Jura, and Normandy, whole banks and reefs 

 of corals are met with in the " brown Jurassic" rocks : in 

 Swabia they are rare. With the depth of the sea the size 

 of the shells is also related ; the Terebratulae and Spiriferi 

 of the lias are twice as large in Calvados as in Swabia ; the 

 Ammonites of the ornati-clay grow here to such a gigantic 

 size that one who has only seen the Swabian specimens can 

 scarcely recognise them again. We need not point out that 

 the materials also of the deposits, and their greater or less 

 thickness, are connected with this point. 



3. The quality of the water. — Apart from the many springs 

 and currents in the sea which carry with them lime, quartz, 

 and other matters to be contributed to the formation of rocks, 

 there are especially two great causes which, sometimes con- 

 jointly, and sometimes in succession, are continually at work 

 contemporaneously forming a stratum with varying charac- 

 ters at different places. These important factors are the 



