758 



SCmNGE, 



[N. S. Vol. IV. No. 99. 



never supposed that any one would attempt to 

 place these beds lower than I had done, because 

 it seemed impossible that such highly organized 

 plants could have flourished earlier than the 

 extreme upper portion of the Lower Cre- 

 taceous. 



It is, therefore, a matter of the greatest sur- 

 prise to me that Prof Marsh should have discov- 

 ered evidence which points to the Jurassic as the 

 true date of the strata in question. His two 

 papers on ' The Geology of Block Island, ' pub- 

 lished in the American Journal of Science for 

 October (pp. 295-298) and November (pp. 375- 

 377), are well calculated to stagger one who has 

 been studying these deposits for eight years 

 and who has visited all the exposures from the 

 Raritan River to Nantucket, usually in com- 

 pany with Mr. David White or Dr. Arthur 

 Hollick, and helped to make the extensive col- 

 lections that they have yielded. It is true that 

 until the present year I had not personally 

 visited Block Island, but Mr. White was there 

 in 1890, and his notes agree with my own later 

 observations. Being a noted watering place I 

 had naturally avoided it, and most geologists 

 who have studied it have been chiefly interested 

 in the glacial deposits that occupy its surface. 

 But lying, as it does, directly in the line of the 

 Cretaceous outcrop, and rising somewhat 

 higher above the sea than most of the other is- 

 lands, it was to be expected that the underly- 

 ing clays would be exposed. I had long de- 

 sired to see them, and in August last I re- 

 quested Dr. Arthur Hollick, of the School of 

 Mines, Columbia University, whose studies in 

 this line, especially on Staten Island and Long 

 Island, are so well known, to accompany me, 

 and after making an excursion to certain criti- 

 cal localities on Long Island, including Mon- 

 tauk Point, we crossed to Block Island and 

 sp \three days in making a careful examina- 

 tion ^ all the exposures. We found the Cre- 

 taceox yxis immediately. It originally occu- 

 pied the northern half of the island. It is 

 clearly visible at the north end of Grace 

 Cove, on the west side of the island, but is best 

 exposed below Ball's Point, on the east side. It 

 has, as on Martha's Vineyard, a local dip to the 

 northwest, due to the action of ice tilting it in 

 the direction opposite to its normal dip. This 



however, was not suflBcient to prevent the Clay 

 Marls, which immediately overlie these clays 

 wherever conditions are normal, from coming 

 into view on the south end of the island, and 

 numerous exposures of these were discovered 

 containing their characteristic molluscan fossils, 

 of which a fair collection was made and sub- 

 mitted to Dr. Whitfield for identification. Fos- 

 sil leaves were also found at many points, but 

 they were usually too poor for safe determina- 

 tion. They were sufllcient, however, to show 

 that we were dealing with precisely the same 

 beds as those of Gay Head, Long Island (Glen 

 Cove), and Staten Island, which have yielded 

 such a large flora, and, therefore, they belong 

 to the Island Series. The characteristic red 

 micaceous clay shales were identical with those 

 found erratic all along the coasts of these islands, 

 often where the clays themselves are below tide 

 level. In Split Rock Cove, immediately east of 

 Black Rock Point, the alternating red, black, 

 and white clays, with a steep incline, simulate 

 very closely those of Gay Head and leave no 

 doubt that they represent the same condi- 

 tions. 



Prof. Marsh does not question the parallelism 

 of all these beds, but refers them all to the Ju- 

 rassic. He says : ' ' An examination of both 

 the Raritan and Staten Island clay deposits has 

 supplied two links in a chain of evidence that 

 I had not before known from personal observa- 

 tion. This chain now extends from the Poto- 

 mac river to Martha's Vineyard, along the 

 natural line of the Jurassic horizon, and indi- 

 cates the Jurassic age of this series of strata 

 beyond reasonable doubt. " * In another place f 

 he says : ' ' The Raritan clays of New Jersey I 

 regard as belonging to the same series as the 

 Potomac beds. ' ' From these statements it seems 

 clear that he regards the Potomac formation as 

 representing one and the same horizon through- 

 out, and believes that it is all Jurassic in age. 



In his important paper just published in the 

 Sixteenth Annual Report of the United States 

 Geological Survey he figures a few Dinosaurs 

 from the Potomac formation, but seems to in- 

 clude none that were not published by him in 

 his paper in the American Journal of Science for 



* Am. Jour. Sci., November, 1896, p. 376. 



t Am. Jour. Sci., October, 1896, p. 296. 



