8 GROVE KARL GILBERT— DAVIS IMEM0,RS [ v A L TI xxt 



contacts with Hall in later years, the memory of his sojourn at Albany while working on the 

 fossil mastodon sufficed to call him back there in 1898, when he was one of the few pallbearers 

 at the funeral of the great paleontologist. 



THE MOHAWK GORGE AT COHOES 



While in Albany, Gilbert, besides working on the mastodon skeleton, studied the gorge 

 of the Mohawk at Cohoes and prepared an account of it which appeared in Hall's report. This 

 is his first essay based on original field observations; it does not read at all like that of a geological 

 catechumenist. He examined 350 potholes in the river bed above the falls; their typical form 

 was that of a " chemist's test-tube;" the deepest had a vertical measure of 23 feet, with a diam- 

 eter of 3 feet. A simple conclusion as to the origin of the potholes is conservatively announced : 

 "In my examination I saw nothing to controvert the theory that they were formed by the 

 grinding action of stones moved by water." The huge pothole in which the mastodon skeleton 

 was found is one of a group of much larger dimensions, in the low upland outside of the river 

 gorge and apparently excavated by other currents than those of the Mohawk. Cohoes Falls, 

 descending 57 feet, he between rapids up and down stream, and are peculiar in that they occur 

 in a series of strongly tilted Hudson River shales of fairly uniform texture; hence the question 

 was raised: "Is it not possible that rapids constitute the normal mode of descent of a river 

 over these upturned shales, and the falls are merely an episode occasioned by preexistent pot- 

 holes?" — the potholes thus referred to presumably being members of the upland group. Many 

 years later Gilbert spoke of this study of potholes as having been of so much interest as to lead 

 him to desire further work in geology. 



Although all these items are of interest, Gilbert's study here is chiefly significant from a 

 novel quantitative method that he invented for determining the recession of the gorge-side 

 cliffs. " Climbing from below, or lowered by a rope from above, " he measured and cut sections 

 of 20 contorted cedars, growing in a cliff and "appearing at a little distance mere bushes, but 

 really very old trees, " which had been dwarfed by starvation in the infertile shales, and of which 

 the roots had been "bared by the waste of the cliff during the growth of the trees. " An average 

 of 6 sections gave 144 rings of growth to an inch of trunk radius, and the estimated age of the 

 oldest tree sectioned was 716 years; yet the trunk of this famished pre-Columbian settler, who 

 must have began his struggle for existence about the time of Thomas a-Becket of Canterbury, 

 measured only 37.5 inches in circumference, or 6 inches in radius. The relation between age 

 of tree and length of bared and exposed root gave a cliff recession of 12 inches a century; and 

 this led to the estimate of 35,000 years as "a minimum for the time that has elapsed since 

 Cohoes Falls were opposite the mastodon pothole. " 2 This laborious method for the determina- 

 tion of cliff recession might have been applied by any patient and painstaking junior under the 

 direction of an experienced master; but that the patient and painstaking junior should himself 

 and on his own initiative have invented the method, as well as applied it, shows him to have 

 possessed exceptionally masterful qualities with regard to natural phenomena, even if he could 

 not master unruly boys in a country school. The thousands of years revealed in the age of the 

 Cohoes gorge by this ingenious determination are hardly so impressive as the evidence that 

 the determination gives of investigational ingenuity on young Gilbert's part. 



HALF A CENTURY OF DIARIES 



During Gilbert's apprenticeship at Cosmos Hall he formed the habit of keeping a concise 

 diary, and this habit was pursued all through his hf e. Brief entries were made in small pocket- 

 books concerning the persons he met and the places he visited; and 51 of these consecutive 

 annual records have been preserved, beginning in 1868 and continuing to 1918; the last entry was 

 made only a few days before his death. It is a great privilege to look over the personal records 

 of such a man, not in the way of peering curiosity but in a reverent spirit, with the memory of the 

 man himself constantly present, and with much of the sadness that one feels when standing alone 



' 21st Ann. Rep. State Cabinet Nat. Hist, [for 1867]. Albany, 1871. 129-148. 



