GEOLOGY OF LAKE PLEASANT QUADRANGLE 39 



such pebbles of quartz and granitic gneiss were noted by the writer, 

 some of them being as much as 4 to 6 inches long. The presence 

 of the pebbles and sand grains in the otherwise typical Trenton 

 limestone is a puzzling phenomenon and the only satisfactory ex- 

 planation which occurs to the writer is that suggested by Kemp 

 when he says ^ : '' The pebbles and sand were derived from the 

 neighboring crystallines and may have been mixed up with the lime 

 l)y floating ice.'' The limestone of this section (ledge), except for 

 the uppermost zone number 5, dififers from that of the small quarry 

 in being generally crystalline and devoid of shale partings. Judging 

 1)y field relations, the quarry limestone is regarded as overlying that 

 of the big ledge and hence we can be sure of a thickness of no less 

 than 14 to 16 feet with neither top nor bottom shown, though the 

 full thickness is probably not over 30 feet. 



Just south of the big ledge there are many large, angular, loose 

 blocks of the limestone, each of eight or ten of these being 10 or 

 12 feet across and 6 to 8 feet thick. In one block 6 feet thick, 

 pebbles of smooth, dove-colored limestone occur in almost every 

 layer. These limestone pebbles appear to have been derived from 

 the underlying Lowville since the Trenton rests by unconformity 

 upon the eroded surface of the Lowville. 



From materials collected by the writer. Doctor Ruedemann has 

 determined the Lower Trenton age of this limestone which con- 

 tains the following fossils : Streptelasma corniculum, 

 Rafinesquina alter n at a, Rafinesquina del- 

 toid e a, P 1 e c t a m b o n i t e s s e t i c e u s, D a 1 m a n e 1 1 a 

 t e s t u d i n a r i a, R h y n c h o t r e m a i n e q u i v a 1 v e, P a c h y- 

 d i c t y a acuta, H o r m o t o m a cf . gracilis, O r t h o- 

 c e r a s cf . j u n c e u m, L i o s p i r a cf . 1 e n t i c u 1 a r i s, 

 Leperditia fab u lite s, Isotelus fragment, and 1 1 1 a e- 

 n u s sp. fragment. 



At the southern end of the belt of Black River-Trenton limestone 

 shown on the geologic map, and west of the southern end of the 

 village, there are many loose blocks of Trenton limestone which, as 

 already stated, indicate concealed ledges close by. After the covered 

 interval (see above) of 20 feet above the Lowville section here, a 

 few feet of Trenton appears to be in place and this is the only case 

 of the kind. A few rods down the creek from the quarry and the 

 Lowville section, hard, limey, black shale marks the base of the 

 Canajoharie shale formation. This shale and the nearby Lowville 



1 Op. cif., p. 15^ 



