19 1 5- ^•O- 12. i HZ STROPHÛMENIDAE OF THE KRISTIANIA REGION'. 9 



the following figures, that represent the section in Asker— Baerura. where 



detailed measurements have been made. 



Downtonic Sandstone (Stage lo) .... 500 metres. 



Ludlow I > 91 .... 200 > 



Wenlock ( » 8) . . . . 130 » 



Upp. Llandovery- ( > 7) .... 150 > 



Low. Handover)' ( > 6) ... 170 » 



Stage 5 50 » 



Stage 4 320 > 



Stage 3 50 » 



State of Preservation of the Fossils. 



The state of preservation of the fossils is generalh' rather poor. The 

 Kristiania region has been no quiet part of the earth's crust during geo- 

 logic time; on the contrary it has suffered much by orogenetic move- 

 ments. The sedimentary rocks have been hardened, the shales in large 

 parts of the region have received false cleavages, and the embedded fossils 

 have not seldom been deformed by pressure. 



Free complete specimens or single valves are very scarcely met with. 

 We usually find an incomplete valve embedded in a matrix so hard that 

 in most cases it is impossible to lay bare the fossil by chisel and hammer. 



The only method of getting at the interior characters of the valves, 

 has generally been to dissolve the shell substance by hydrochloric acid 

 and then study the mould of the interior thus laid bare As the matrix 

 of the fossils in the majorit\- of cases, however, is hraestone, pure or 

 argillaceous, even this treatment is often very difficult to use with profit 



