386 GEOLOGY OF THE SECOND DISTRICT. 



are no falls or uplifts of any magnitude, the whole thickness is nowhere exposed, unless at 

 and below Brownville. Here it is slightly broken and elevated by an uplift, giving the mass 

 a dip to the northeast and southwest, and forming an indistinct anticlinal axis. The force 

 producing this uplift, elevated the whole mass higher upon the south than upon the north side. 

 Just below Brownville, the drab colored layers belonging to the birdseye appear ; and in one 

 of the strata, I found the orthis which is so abundant at Chazy in the same position. In one 

 of the strata above, cytherinffi in large individuals are not uncommon. 



Isle La Motte Marble. 



Resting upon the birdseye at the base of the cliffs at Watertown, is a mass of black lime- 

 stone about eight feet thick. It is remarkably thick-bedded ; in fact it appears to be one 

 stratum, tlic divisional planes being exceedingly obscure. This is the same wherever this 

 rock occurs. At Isle La Motte, where it is about twelve feet thick, it has been blasted 

 tlrrough as if it were one continuous stratum. 



At Watertown, this rock is broken, or seems to be formed of lumpy masses ; such at least 

 is the case wherever it has been exposed in the banks of the river, and in this respect it differs 

 from the same rock at Glen's-Falls and Isle La Motte. It is black, fine grained, without 

 shaly matter, but is disposed to break into irregular masses, and hence it appears unsuitable 

 for the purposes for whicli it is so valuable at other places. It is here called the Seven-foot 

 tier, and is quarried for walls, and a variety of purposes of a coarser description. 



The character of this mass connects it rather with the birdseye than with the trenton lime- 

 stone, between which two it lies. I have never observed the fossils of the trenton in it ; but 

 a columnaria, and one or two species of large orthoceratites occur in it. The combined facts 

 in relation to this mass seem to indicate that it is the terminating mass of the limestones below 

 the trenton, or that it is not the commencement of that order of things which succeed and 

 follow in the latter rock. From its compactness, we find the fossils difficult to procure, and 

 none of them in a state fit for illustration by figures, except the columnaria whicli has already 

 been placed before the reader (p. 276, Fig. 73, No. 2). 



The value of this stratum at other places in the Second district, encourages me to hope, 

 that in the vicinity of Watertown, it may be found in a state suitable for marble. It forms 

 for an inconsiderable extent the surface rock ; it merely crops out beneath the trenton, with- 

 out extending beyond it. The caves of Watertown appear to have been excavated in this 

 mass, and they were probably formed at the same period as were all the other surface excava- 

 tions. At a few points, the removal of this rock has caused the trenton to cave in, and form 

 upon the surface depressions more or less conical. 



