Limestone of Bolton, fyc. 



309 



In my own opinion, there can be little doubt that this want of strat- 

 ification results from the agency of granite. At any rate, if this be 

 admitted to be a rock of igneous origin, its contiguity to a bed of lime- 

 stone, while yet in a melted condition, will explain the obliteration in 

 that bed of the stratified structure : and I can imagine no other cause 

 that will explain it. I did not observe, indeed, the contact of granite 

 with the limestone, except at the principal, or north quarry in Bolton. 

 But at that place the stratified structure is more completely destroyed 

 than at any other. Yet I did not search for granite in the vicinity of 

 the other masses of limestone, as my attention was not till recently 

 particularly called to this subject ; and probably it maybe found near 

 most of them, if not concealed by the soil. Or if not, there is evi- 

 dence that gneiss has been subject to a degree of heat little inferior 

 to a melting heat. 



Nearly all the limestone at these quarries is coarsely granular and 

 highly crystalline. It is almost uniformly fetid also ; sometimes so 

 much so as to produce nausea when struck, in a stomach of much 

 sensibility. This was very unexpected to me in limestone of such 

 great relative age ; the fetid limestones of Europe being almost ex- 

 clusively found in secondary rocks. 



Although but a single bed of limestone is marked upon the map in 

 each of the towns mentioned above, yet in most of them there are 

 several ; some of them one or two miles distant from one another. 

 In Bolton are two, in Boxborough one, in Littleton three, in Acton 

 one, in Carlisle two or three, and in Chelmsford two or three. Not 

 improbably others exist in the neighboring towns, which escaped my 

 notice. 



The simple minerals imbedded in this limestone are numerous and 

 interesting. In general, specimens from the different localities can- 

 not be distinguished ; though particular minerals are more perfectly 

 developed at one place than at others ; and one or two, perhaps, are 

 found only at one quarry. The most common and abundant mineral 

 is scapolite. It occurs both crystallized and compact ; and at all the 

 localities above referred to. The crystallized variety is most abun- 

 dant at Bolton, Boxborough, Chelmsford, and Littleton ; particularly 

 at the two first named places. The crystals are sometimes transpar- 

 ent, more commonly opaque and white, having begun to decompose. 

 Sometimes the crystal exhibits the primary form, or a right square 

 prism, acuminated by four planes set on the lateral planes. More 

 commonly, however, the lateral edges are slightly truncated. Some 



