I06 OLAF HOLTEDAHL. M.-N. Kl. 



often been abundant also where a relatively great sedimentation of fine- 

 grained terrestrial material has taken place. It is not only small forms 

 or small specimens of larger ones that are found in shale. One of the 

 largest specimens found, the Raf. (?) Schmidti (depicted pi. Ill, fig. i) lies 

 e. g. in shaly matrix and the shale specimens of forms like Lept. rhom- 

 boidalis, Strophomena Asinusi, Schuchertella pecten and others are as well 

 developed as specimens in limestone of corresponding stage. 



From the finegrained black shales only, with the well known characters 

 of the graptolite shales, the Strophomenids are nearly or totally absent. 

 In the graptolite bearing Ogygia shale (4 a a) no Strophomenid is found at 

 all and in parts of the Trinucleus shale of 4 c and in the Monograptus 

 shales of 8 a — b of the Bundefjord district we may at the most find small 

 Plectambonites specimens. The foul bottom (and greater depth) have 

 certainly not been favorable for the Strophomenids. 



The specimens which occurs about equally commonly in equally large 

 specimens in both limestone and shale are evidently the relatively long 

 ranging fossils, like Strophomena Asmust, S. antiqiiata and above all Lept. 

 rhomboidalis. This was what could be expected, because the circumstance 

 that a fossil is found from many horizons, consequently comparatively fre- 

 quently found, also makes it probable that it is found in different sorts of 

 rock. Yet the fact certainly is connected also with a comparatively large 

 adaptability to different biological conditions being relatively well developed 

 in these long lived species. 



In his interesting study on »Cambrian and related Ordovician Brachio- 

 poda — a Study of their inclosing Sediments« ^ L. D. Burling also found 

 a large percentage of those brachiopods which occur in different types of 

 sediments to be long lived forms. He states p. 428: »Species common to 

 different sediments are shown on analysis to exhibit a more or less similar 

 latitude in their stratigraphie range; to be exact, 44 per cent of the species 

 occurring in more than one type of sediment (141) have been identified 

 from more than one of the three main divisions (Lower, Middle, and 

 Upper) of the Cambrian.« Of the 12 Norwegian species found in both 

 limestone and shale not less than 8 (67 per cent) occur through more than 

 one stage. On the contrary, of the forms restricted to one type of sedi- 

 ment (also those from stage 5 included) only 9 out of 39 are found in 

 more than one stage. 



^ Bull. Geol. Soc America. Vol. 25, 1914. 



