Geology of Antigua. 83 



from the partial examinations already made, that they are due, 

 not to a single cause, but to a combination or rather a diversity of 

 causes. For example, some of the finest specimens of jasper are 

 found in trap veins, and in the neighborhood of trap rocks. There 

 can be no doubt, therefore, that these are to be ascribed to igne- 

 ous agency, converting an aqueous rock into this beautiful sub- 

 stance. Lyell, De La Beche, and other authors, have detailed 

 similar facts occurring in other parts of the world. But in regard 

 to the chert deposits, and the immense quantities of petrified 

 wood connected with them, I think we must look for the agency 

 of some other cause. The circumstance that those beds contain 

 shells, either marine or fresh water, or both, is indubitable evi- 

 dence, that they are an aqueous deposit. But whether they were 

 originally deposited in their present form, or whether they are al- 

 tered rocks, is a question about which there may perhaps be some 

 difference of opinion. It is perfectly obvious, that since their 

 formation, they have been subjected to the action of an internal 

 force, which has thrown them up and broken them in pieces, and 

 perhaps in some degree changed their constitution. The island, 

 also, in the trap formation and in the contiguous altered rocks, 

 affords the most ample evidence of comparatively recent igneous 

 action on a broad scale. The position of the strata, also, being 

 conformable with those of the clay formation and not separated 

 by any definite lines, might be considered as favoring the suppo- 

 sition, that they both belonged originally to the same class of 

 rocks. Though I know of no example on so large a scale, where 

 rocks of this description can clearly be traced to such an origin, 

 yet cases of a more moderate extent are not unfrequent. And if 

 we admit, with Lyell, that all the earlier slates are merely meta- 

 morphic rocks, changed from sandstone and other fragmentary 

 deposits into their present semi-crystalline forms by internal heat, 

 we seem to have an acknowledged cause adequate to the effect. 

 But, however sublime and interesting such a conception may be, 

 we are not perhaps yet prepared to admit it among the sober 

 truths of geology. But independently of this objection, there are 

 peculiar circumstances, which seem to refer the beds in question 

 to another origin. I have already remarked that the shells im- 

 bedded in them show, that they were originally deposited from 

 water ; and the fact that these shells are peculiar to the chert — 

 that is, are not found in strata of the clay formation — seems to be 



