'I have exposed, or assisted in exposing, every interment in the district, described in this volume. I observed everything in situ, and with my own hands removed the relics. I have attempted to tell in a plain way what I have seen.'

Definitely a man of the Wolds engaged in research in his neighbourhood.
John and his brother Robert in their first ten years of collecting geological and archaeological specimens in the neighbourhood of Fimber had only two main rivals as collectors of such specimens - Edward Tindall of Bridlington and George Pycock of Malton. During this period the Mortimers trained many of the farm servants in the district to distinguish and keep for them all the specimens they could find. They exhibited these specimens in cases in their offices at Fimber. This collection consisted mainly of chalk fossils and a few stone and flint tools.

In the period from 1861 to 1896 more collectors entered the field and John Mortimer tells at one time there were as many as thirteen noted collectors visiting the area. These collectors often bought specimens from the field labourers whom the Mortimers had trained, and bid more for the items and thus ran up the prices. Farm servants became quite ready to take advantage of the extra prices to be obtained from the rival purchasers. The Mortimers were obliged to distribute handbills, offering rewards of money and a free pass to the Leeds Exhibition of 1866, to those who would supply them with the greatest number of articles.

Edward Tindall of Bridlington was a keen collector but was always ready to dispose of items to those who wished to buy. On his death in 1877 part of his collection was bought by Mr. Robert Gatenby of Bridlington. Mr. George Pycock of Malton sold his collection to Dr. Rook of Scarborough to be placed in a private museum.

The Rev. Canon Greenwell conducted many excavations in our district himself but also amassed a large number of valuable specimens which had been gathered from the surface of the Wold hills. In July 1896 the canon sold his collection to Dr. Sturge of Nice.

Mr Samuel Chadwick of Malton was a collector of fossils and implements, many of which went to the Malton museum when he emigrated in 1895
Implements of flint collected by J.R. Mortimer included, hatchets, scapers, knives, sickles, a fine example of which was found at Kilnwick, saws, drills, sling stones, hand weapons, grinders, polishers, arrow points and heads of javelins.

Flint Jack, or to give him his proper name, Edward Simpson, as a boy had been engaged as a servant by a Whitby historian, Dr. Young. He had accompanied him on many of his fossil hunting expeditions. The young man became intrigued with the fine workmanship in the flint arrow heads he found. he made many unsuccessful attempts at first to copy them from raw material he found in the boulder clay on the beaches.
The market was just right at this time for the creative Flint Jack, as many collectors were willing to pay higher prices for the specimens of flint and stone found on the Wolds. With an eye for business he visited museums and collections to find out which artefacts were in demand and studied their designs.

Flint Jack worked on perfecting his skills of making duplicates of the flint implements until he became an expert in his craft.
In 1866 the Malton Messenger exposed 'Flint jack', alias Edward Simpson, to its readers:

'Jack's dupes are found alike in the curator of the British Museum and in the curiosity fancier of the Yorkdhire village ….. all alike victims in the first instance to the cleverness of an arrant rogue, and there are few scientific men who have not been constrained, at one time or another, to confess themselves 'done' by the artful dodger, and plausible subterfuges of the Prince of Counterfeiters - Flint Jack.'
Jack continued selling his forgeries on his travels and keeping one step ahead of the law, and sometimes joined in archeological digs. Antiquarians throughout the country, however, eventually became aware of Flint Jack's activities and several major collections were shown to contain his home made replicas. The late Mr. Eric Grantham, whose father had a private museum at North End, Driffield, was at one time in possession of some scrapers and arrow heads forged by Flint Jack.
When Jack had been rumbled he continued to roam the country and found that many of his previous customers could laugh off the way they had been deceived. This helped to make Jack a celebrity, and he demonstrated how he made his duplicates to a gathering of Geologists in London, and the audience were keen to buy the ancient flint tools he knapped before their eyes.

Jack, most likely, could have done very well selling his forgeries, but it seems thst the demon drink got hold of him and his last years were spent in poverty either in gaol or the workhouse.
John Mortimer observed that the various implements of flint he found in the barrows, in immediate connection with the body, appeared to be perfectly new, whilst those not associated with an interment, had evidently been in use.