428 Expedition to the 



which occupies so large a portion of the interior of our con- 

 tinent includes a vast area of surface extending through 

 twenty-five degrees of latitude and sixty of longitude. We 

 confine our attention to that portion of it, which the state of 

 facts at present known, enables us to speak of with some de- 

 gree of confidence. This portion may be considered as oc- 

 cupying the area of a large triangle, whose base is a line run- 

 ning from Montreal, in Lower Canada, S. W to a point near 

 the outlet of the river Sabine, the western boundary of the 

 state of Louisiana. The summit would be at the sources of 

 the Saskatchawin which are west of north from the mouth of 

 the Sabine, and north of west from Montreal. The Rocky 

 Mouiitains on the southwest, and the Alleghanies on the 

 southeast mark the limits of the secondary in those directions. 

 Its extent towards the north and northeast is as yet unknown. 

 In the wide space included within these lines, we know of 

 but one exception to the remark, that all the rocks found in 

 place are secondary. This is the instance of the Ozark Hills 

 traversing the horizontal strata from southwest to northeast 

 somewhat in the manner of a whin dike. A proitiinent pe- 

 culiarity of this range is the prevalence among the secondary 

 strata of crystallme substances, and what are called rocks of 

 chemical deposition, and the alternation of these with beds 

 and strata whose integrant particles bear evident marks of 

 having been worn and rounded by mechanical attrition. Ap- 

 pearances of this kind are observed in all formations of se- 

 condary rocks, but it is believed, are in few instances, as ex- 

 tensive or as numei'ous as in this. It is well known that the 

 ores of lead so abundant in many parts of this range occur in 

 the uppermost strata of horizontal sandstone, or in primary 

 soils superimposed upon those sandstones. It has been sug- 

 gested that these ores of lead may have been brought down 

 in the alluvion of rivers from some more ancient and elevated 

 region,* but any one who shall examine them in connexion 

 with the substances with which they are now found asso- 

 ciated, will be convinced that their origin has been contempo- 

 raneous to the deposition of the sandstone. That the sparry 

 limestones, the crystalline sandstones, and perhaps the ores 

 of lead, (almost invariably found in the form of crystals,) 

 have been deposited from solution in water, is highly proba- 

 ble, and that these depositions must have taken place in con- 

 nexion with circumstances not unfavorable to animal life, is 



* Maclure, p. 57. 



