MECHANICAL DEPOSITS IN MOUNTAINS, &C. 13 



III. 



On thefuppofed Exiftence of Mechanical Depofits and PetrefaSiions 

 in the Primitive Mountain*, and an Account of Petrefaclions 

 illicit have been difcovered in the nezveft Fl'olz Trapp formation. 

 By Mr. Robert Jameson. Communicated by the Author. 



vJ'UR globe, according to the Wernerian geognofia, even The primitive 



during the depofition of the newer primitive ftrata, appears to ™ c ed 9 f J^ 'J* 1 ' 



have been covered to a great height with water, as is evinced great depth of 



by the want of all mechanical depoiit *. After the precipi- **" ™ hich <;0- 

 • r r • itirj vered the globe. 



tation of thefe great rock formations, the level of the water 

 became fo low, as to allow it to act mechanically upon the fub- 

 jacent rocks ; this occasioned the firft mechanical depofition, The tranfition 

 which difcovers itfelfin the tranfition rocks (Ubergangsge- rock - s when the 

 biirge). Nearly at the fame time organization commenced, at wn i c h time *° 

 as it is in the tranfition rocks we find the firft traces of organic organization be- 

 remains : thefe are generally zoophytes and fea plants, a facl 

 which goes deep not only into geology, but natural hiflory. 



Profeflbr Play fair, in his illufirations of the Huttonian the- j n fiances of me- 

 ory, mentions feveral infiances of mechanical depofits and # c hanical depofits 

 petrefaciions which have been difcovered among the primary offered by Pro-* 

 ftrata, and from thefe he concludes, that no fuch feries of ftrata feflor Hlayfair. 

 as the tranfition exift. I fhall now examine the Statements he 

 has given; and firft refpecting the occurrence of petrefactions 

 in primary mountains. 



At page 164 he obferves, "Another fpot, affording in- shells in primi- 

 ftances of fhells in primitive limeftone, is in Devonfhire, on , tlve iJm . el ? one > 

 the fea fhore, on the eaft fide of Plymouth dock, oppofite to f pjym u" n f 

 Stonehoufe, I found a fpecimen of fliiftofe micaceous lime- & c. 

 ftone, containing a (hell of the bivalve kind ; it was ftruck off 

 from the folid rock, and cannot poflibly be confidered as an 

 adventitious foffil. Now, no rocks can be more decidedly 

 primary than thofe about Plymouth ; they confift of calcareous 

 ftrata, in the form either of marble or micaceous limeftone, 

 alternating with fhiftus of the fame kind, which prevails through 

 Cornwall to the weft, and extends eaftward into Dartmoor, 

 and on the fea coaft as far as Berry Head. Thefe all inter- 



* The exception to this in tire fienite formation I explained in a 

 former paper, 



fea 



