Alvar - leveled and massiv limestone, planed by ice age glacier. Non to little soil development during last few thousand years create an envirement for very specialized plant communities.
Those stronger cracks have to do with the structure of the limestone, the finer scratches origin from glacial movements during the last ice age.

More about Alvars:
english - en.wikipedia.org/wiki/Alvar
deutsch - de.wikipedia.org/wiki/Alvar_(Landform)

Two further sites about Canadian Alvars worth seeing, you'll find here - very nicely written and garnished with most beautiful images:
- floraofohio.blogspot.com/2017/04/the-bruce-peninsula-part-vi-alvar.html (all seven parts about Bruce Peninsula are worth to look at - in my opinion ... and not even mentioning the rest of this interesting site)
- www.meanderphotography.ca/Alvar