ORDOVICIAN FAUNAS IN LAKE CHAMPLAIN VALLEY 457 



though a separate outcrop of 15 feet of Utica strata occurs a short distance to the 

 north ; also on the opposite side of the lake at Addison Junction, New York. 



SHOREBAM 



East of Larrabee point there are no important outcrops until Shoreham is reached , 

 about 2)^ miles west of the lake. The ridges of strata here exposed embrace the 

 entire lower Ordovician.* They are much sheared and crusiied, althougli. retain- 

 ing remnants of a fauna whicli was very abundant and which corresponds in the 

 upper portion to that of the base of the Larrabee Point section. 



CROWN POINT 



The extreme end of Crown point, Essex county, New York, I25 miles north of 

 Larrabee point, affords the next and for detailed study tire most satisfactory sec- 

 tion. All four divisions of the Oalciferous, as classified by Messrs Brainerd and 

 Seely, overlie the Cambrian witli a thickness of 350 feet, followed by all three divis- 

 ions of the Cliazy, aggregating 305 feet thick. The latter terminates within the old 

 French fort (Fort Frederick) near the end of the point, with a bed of silicious sand- 

 stone or quartzite, wliich is also seen at Valcour, at the upper end of the lake. The 

 Black River here attains a thickness of 71 feet 3 inches and contains an abundant 

 fauna. Following this series a beach covers 30 feet of horizontal distance and the 

 transition beds to the Trenton proper, althougli if no fault occurs in the interval 

 the missing thickness, as calculated on tlie dip of 8 degrees north 40 degrees west; 

 is only 4 feet. Above the Black River a continuous series of 100 feet of alternating 

 compact, sandy and shaly layers, all quite thin, is presented, which affords con- 

 stant faunal variations and numerous interesting assemblages of forms. Neai'ly 

 the entire middle and lower Trenton fauna of the region is represented in this sec- 

 tion. After disappearing under the lake, which is very narrow at this point, the 

 Trenton reappears, with beds belonging an unknown distance above the former, 

 followed by the Utica slates, but separated from them, however, by superficial 

 deposits. The Utica slates may be followed in outcrops at intervals for 8 miles 

 along the Vermont shore north of this locality, to Arnold bay in Panton. A little 

 over 2 miles north again on Button island, near Vergennes, Vermont, is a remark- 

 able exposure of the Black River. In the lower portion of the section is a thin band 

 containing inyriads of Leperditia fabuliles in perfect state of preservation, and near 

 the top a sharply defined coral reef band made up entirely of Columnaria alveo- 

 lata and Stromatocerium rugosum. The Trenton is exposed in small outcrops on the 

 neighboring shore, and the Utica on Otter river, between the lake and Vergennes, 

 but no continuous section is afibrded. 



PLATTSBURG AND CUMBERLAND HEAD 



On Crab island, nearly opposite the hotel Champlain, beds of tlie middle Tren- 

 ton, having a thickness of nearly 100 feet, are shown containing a fauna, among 

 which Isotelus gigas and several species of JEndoceras occur in prolific quantities and 

 of large size. This series of beds, extending up into the Utica, reappears on the 

 shore just south of Plattsburg, although on account of faulting no complete section 

 can be obtained. 



Beginning at the head of Cumberland bay, and extending all the way around 

 Cumberland head and thence up the shore around Point-au- Roche is a series of 



* E. Brainerd and H. M. Seely : Bull. Am. Mus. Nat. Hist., vol. iii, 1S90, pp. 3-5. 

 LXV— Bull. Geol. Soc. Am., Vol. 10, 1898 



