. III. DIST. CHAR. Soil. 165 



The volcanic f consist of lava, pumice, &c. the 

 ejected matter of still existent volcanos. 

 b. Structure. 



According to which the soil is either continuous 

 or stratified. 



A. 134. A CONTINUOUS SOIL ( Solum 

 continuum) consists of a mass of mineral matter not 

 divided into beds or strata. 



Obs. Primary soils frequently come under this 

 division ; as their rocks do not commonly exhibit 

 parallel joints or other external marks of stratifica- 

 tion f f . The most modern of the secondary soils 



t The reader will remark, that we have confined our notice of 

 volcanic soils to those of very modwn production. We by no 

 means, however, subscribe to the opinion, which some mineralo- 

 gists hold, that the vestiges of extinct volcanos are not discover- 

 able among the more ancient strata. Indeed, there is reason to 

 suppose, that volcanos have existed during every period of the 

 earth's formation ; and, that the consequences of their eruptions 

 may be traced among the most early mineral productions, even 

 such, perhaps, as are truly primeval at the same time, we cannot 

 attribute to their operations, those extensive effects, contended for 

 by some modern geologists. 



f f We conceive, however, that this arises, in some cases, from 

 the immense thickness of a stratum ; which may be such as to 

 conceal its connection with other beds from observation. Thus the 

 large blocks or masses of granite, which often constitute pri- 

 mary soils, may be only the detached or shatter parts of an enor- 

 mous stratum, whose extent prevents its real form, as well as itt 

 dependance on similar strata, from being traced. 



