^00 On the Orthoc'eratiies of Scotland. [Mabch^ 



■which the)- are imbedded, and the relation of these rocks to the 

 strata which constitute the crust of the globe. 



By attending to the first of these objects, or to \vhat may be 

 termed the si/siematic history cf petr'ijactions, we avoid all am- 

 biguous references, and introduce accuracy into our descriptive 

 mineralogy by the formation of a general language. Had this 

 department been studied with greater care, geologists would not 

 have been so frequently perplexed in accounting for the phenomena 

 of nature. How often do we hear it asserted that the plants, 

 corals, and shells, which are found in a fossil state in the rocks of 

 this country, bear the strongest resemblance to those of Africa and 

 India ? Yet when these are subjected to a close examination, they 

 are found to be specifically distinct, and the distracted philosopher 

 is saved the trouble of deluging the earth by a comet, or of changing 

 its axis of motion. Naturalists were long employed in searching for 

 the means which transported the monsters of the equatorial forests 

 to the frozen regions of the north, until the systematic accuracy of 

 a Camper and a Cuvier proved the fossil elephant to be a new 

 species, differing in form and character from the elephants of 

 Africa or India. Before the physical distribution of petrifactions 

 can be investigated with success, the particular species must be 

 previously ascertained. 



The second object deserving attention in the history of petrifac- 

 tions is the examination of their present condition, with the view of 

 ascertaining the various changes which they have undergone. This 

 may be termed the chemical history of petrifactions, as it makes us 

 acquainted with the operations performed in the great laboratory of 

 Nature, and enables us to comprehend the intricate process of 

 mincrahzation. 



The third object of importance in the history of petrifactions is 

 their situation, the strata in which they are imbedded, the parti- 

 cular formations in which they occur, and the organic remains with 

 which they are associated. This may be termed the geognostic 

 history of petrifactions, and will be carefully studied by those who 

 are anxious to trace the revolutions which the surface of the earth 

 has undergone, and the various catastrophes which have befallen 

 the form.er tribes of animals and vegetables. This arrangement 

 will be adopted in the following paper, after having made a few 

 preliminary remarks. 



Numerous species of spiral multilocular shells belonging to the 

 genus miutilns of LinnHeus ha%e been found in a fossil state in the 

 strata of Britain ; but the mineralized remains of the straight shells 

 forming the second family of the Linnsean nautili, and included in 

 the modern genus orthocera, arc of rare occurrence. Lhvvydd, in 

 his Ichnographia Lythophylacii Britannici, p. 89, informs us that 

 they are found in Gloucestershire, Oxfordshire, and Northampton- 

 shire. He dcscriiies them under the title alveolus, and appi^ars to 

 have obtained them from alluvial strata. The late Kev. David Ure, 



