GEOLOGY OF THE VICINITY OP LITTLE PALXS 25 



cover of the younger rocks. These are at a greater distance from 

 the pre-Cambrian outcrops than are the exposures at Little Falls, 

 and this increased thickness is no doubt due to overlap, as is the 

 diminished thickness in the other direction. It is therefore held 

 that there is nothing which can be mapped as a formation, corres- 

 ponding to the Potsdam, in this portion of the Mohawk valley, 

 but that the Beekmantown rests everywhere on the pre-Cambrian, 

 overlapping on its surface. It is by no means impossible that the 

 Potsdam may come in below, farther away from the present pre- 

 Cambrian edge of outcrop, but there is yet no decisive evidence 

 that this is so. 



It is also possible that the base of the Beekmantown, as exposed 

 at Little Falls, may be of Cambrian age. This can only be deter- 

 mined by fossils, and as yet these have not been forthcoming in 

 sufficient number and variety to settle the question. 



Beekmantown formation.^ The Beekmantown rocks are best ex- 

 posed about Little Falls, Middleville and Diamond hill, though 

 presenting numerous outcrops elsewhere. In the main, they con- 

 sist of a gray, more or less sandy dolomite. Occasional layers are 

 very sandy and sometimes even pebbly, and such layers are not 

 confined to the base but may appear at any horizon. Some sandy 

 layers show bright, glittering cleavage faces when broken. Such 

 layers are found in the formation all about the Adirondack region, 



^The paleozoic rocks of the Mohawk valley have been much studied 

 and described, and the writer's work has added little to our knowledge 

 of them except .for some structural details. The main pui-pose of the 

 work was the study of the pre-Cambrian rocks; and, since the prosecution 

 of this work required considerable traversing of the rest' of the area, it 

 seemed a pity not to grasp the opportunity to delimit all formation bounda- 

 ries on the accurate base of the recently published new map. The more 

 important papers touching on the stratigraphy of the immediate district 

 are as follows: 



Clarke, J. M. U. S. N. Y. Handbook 15. p.60-63 



Barton, IT. H. N. T. State Geol, 13th An. Rep't. 1893. 1:409-29 



N. Y. State Geol. 14th An. Rep't. 1894. p.33-53 



Hall, James. N. Y. State Geol. 5th An. Rep't. 1885. p.8-10 



Prosser, C. S. Am. Geol. 25:131-62 



N. Y. State Mns. Bui. 34, p.469-70 



Prosser & Cumlngs. N. Y. State Geol. 15th An. Rep't. 1895. p.632-37 



Vanuxem, L. Geol. N. Y. 3d Dist. 1842. 



